We at Maximus Chillers will optimise the efficiency and take years off the life of your plant with preventative chiller maintenance.
News Article No.9
The first thing our engineers check at the start of the maintenance is the chiller control panel. In here he checks:
The alarm history is analysed in sequential order to build up a picture of the last maintenance period.
The various levels of password accessed menus are checked and adjusted for efficiency and to eliminate any spurious trips on the running of the chiller.
We make a note of the compressor run hours on our detailed Tick Sheet. Bearings on centrifugal compressors and valve gear on reciprocating compressors are changed at pre prescribed intervals as defined by the manufacturer. This is to prevent an expensive failure and the resulting remanufacturing of the compressor.
Each one of these is popped from its holder and the continuity checked with a multimeter. This is maintenance the right way round, instead of run testing and following the fault back to the fuse.
Each of the breakers is tested to ensure it will function correctly when it needs to.
RCD’s work by detecting current leakage to earth. It monitors the difference between the live and neutral poles. As above these are tested on each visit.
The settings and dead band (the difference in pressure between cut out and cut in) are checked and adjusted on each visit. Sometimes due to malfunctioning controls or condenser condition, fans can be manually left off or can be forced on. Not the best running condition, but we will keep you up and running until we send out the new parts. Where this is a bespoke manufactured condenser, we have the best lead time available.
As above, the low pressure switches are checked and adjusted as need be. The seasonal and varying load conditions affect the saturation point of the refrigerant in the evaporator. This can cause untimely trip outs when the plant is otherwise running in optimum efficiency.
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The coefficient of performance is the cooling effect compared with the electrical energy supplied to the chiller. It is represented in a ratio, for example 6:1. That is six times more cooling effect compared with the electricity supplied. The higher the cooling effect relative to electricity supplied, the lower the cost in electricity. The ratio is often divided by 1 to show as just a number- in this example 6. The cooling effect is measured in kj/kg and the electrical supply is represented in kw/h.
A chiller system would have a COP of less than 1 if not for latent heat. Exploiting this hidden heat when both evaporating and condensing the refrigerant is one of the founding principles of the basic refrigeration cycle. It takes a lot of heat added to the system to get the refrigerant to boil, then the same amount of heat is rejected from the condenser in the liquification of the refrigerant.
A lot of basic things routinely drag down the efficiency of a chiller system. Just with the effect of our engineer attending site to carry out the maintenance- he will keep the COP optimised. Here are some of the system checks and procedures he carries out:
When a compressor never goes off due to refrigerant shortage, there is a dramatic increase in electricity consumption. Also, the system will not have very much cooling effect. Continuing like this will cost more money and achieve little.
Basic condenser maintenance will improve the subcooling values. These readings will be taken at various load and ambient conditions at different times of the year. This is so we can build up an understanding of the plant. We carry a wide range of chemicals for the maintenance of your condenser. These chemicals are carefully selected so that they do not damage the condenser causing leaks. Condenser fans also cause a poor COP:
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With some basic chiller designs, the chiller condenser fans come on and off forwards and backwards at different pressures. This means that when other fans have failed, or are stuck going backwards- the one on the end comes on with the higher pressure then blows to earth. This is due to the ingress of water in the year it did not run.
The above design means that there are fluctuating pressures in the condenser. This causes continuous expanding and contracting of the copper tubes. These copper tubes rub against the steel frame which is holding them in place- causing reoccurring leaks. Another reason for repeated leaks on the condenser is the vibration issue of the fans banging on and off. Add into this equation a cheap, flimsy frame that develops its own resonance- you then have an un ending problem.
Part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere is that we can source any fan speed controller from our fast supply chain. This remedies the problem, as fan speed controllers bring all the fans on together at different speeds. Therefore, extending the lifespan of the fan and maintaining an efficient coefficient of performance.
Most air cooled chillers use axial fans. They suck the air through the condenser and reject it upwards and away from the chiller. Ducts are often fitted to help this process. Scaffolding is erected to provide safe access to engineers.
Radial fans are also called centrifugal fans or blowers. They are very popular in server rooms where air is blown down into a mezzanine floor and up through the racks. They are also used outside in chillers where they blow out and away from the chiller. They are usually driven by belts which require regular inspection and maintenance.
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In the photo, the controller shows R134a refrigerant and the 8.3° of superheat as calculated by the program. This superheat may look at first to be okay, but when considering the compressor loading and expansion valve- it points towards a system issue. Our engineers diagnose if the issue is related to a component or a refrigerant shortage.
HFC refrigerant which has a chemical name of Tetrafluoroethane or CF3CH2F. It has low toxicity which is good for the health and safety or our engineers. It is not combustible, but other chemicals are made as a result of a fire. It is non corrosive too, which extends the lifespan of the pipework and components around the system.
This refrigerant is widely used as a replacement for HCFCs, such as, R22 used in centrifugal chillers. It is only one fluid, where as the other popular HFC refrigerants are blends. These blends fractionalize in a flooded condenser or evaporator. That is to say: one or two of the refrigerants in the blend separate out and do not continue their cycle around the system. The chiller now has the wrong refrigerant circulating around the system for the application temperature. Extreme running faults follow, such as, ice on the compressor, suction pipe and expansion pipe. This is as a result of the refrigerant pressures and temperatures being outside of nominal conditions.
A global warming potential of 1430 is considered to be high. Therefore, the refrigerant is being phased down to 21% by 2030 in line with F-gas guidelines. These guidelines are in accordance with the European Union and the Kyoto Protocol. Because of the regulations for the handling of fluorinated gas, our engineers attend college to learn how to decant the refrigerant safely. We then ship it to the recycling centre for disposal. A waste carrier note being completed each time to track the refrigerant from dispatch to disposal. Finally, F-gas leak tests are carried out and recorded on each visit. Maximus Chillers completes the picture.
Air Cooled Chiller Planned Maintenance
To read more about chiller control panels hit the Tag at the top of the page.
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A rainy day for a chiller breakdown for our engineer in the North West.
News Article No.8
Our customer called us out because he was having electrical faults with the chiller. The power supply to part of the panel had gone down and he required our assistance. Our engineer found a blown fuse which he replaced and tested operation- it blew again. Using his multimeter, he followed the diagnosis though to an earth fault on the flow switch…
The flow switch vapour seal had failed allowing rain water to ingress. This caused an earth failure on the 240v control circuit, and so blowing the fuse. The customer raised an order forthwith and so our engineer replaced the flow switch with the stock from his car. Each of our engineers keeps a range of flow switches for a variety of applications…
Where water system chemicals are corrosive, we carry corrosion resistant flow switches. This type has a longer working life due to the use of stainless steel. They are more expensive due to the higher manufacturing costs, but they are worth the money as they are less likely to fail, causing a potential loss of production.
This was the type fitted by our engineer on site in this news article. It has been developed and tested across a range of adverse weather conditions including freezing conditions and heavy rain. The electrical and switching compartment is protected by a sealing gland to keep the weather out. A rubber ‘o’ ring provides the seal into this compartment.
Some applications have the flow switch located inside the building in the plant room with the control cable extending out to the chiller controls. Another configuration allows for the flow switch to trip out the building controls and so dropping out the run signal to the chiller. In either case there is no need for weather proofing. This kind of flow switch is cheaper due to the lower construction costs.
Some water systems operate at considerable pressure. Therefore, high pressure flow switches have been developed for this application. They are capable of preventing water ingressing from the water system and into the electrical and switching compartment.
Our engineer carried out testing and adjustments to the flow switch to ensure that it ran reliably. He achieved this by monitoring the water system readings and measurements against the design specifications of the switch. When he got it to settle down, he replaced the fuse and ran tested the chiller...
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The condenser fans were not coming on at all at first and later only slowly. They are controlled by a fan speed controller which is sensitive to pressure. A minimum value of volts is supplied to the fans, so as to prevent stalling and over heating of the internal motor windings. The fans were found to be in good working order, so he decided to turn his attention to…
There was found to be a lower pressure and so a lower temperature in the condenser. After careful fault finding and diagnosis involving putting the pressures and temperatures into a calculator, our engineer decided that the chiller was running short of refrigerant. This is consistent with Charles’s Law of Constant Volume: one of the fundamental scientific principals of how a chiller works- the higher the pressure- the higher the temperature/ the lower the temperature- the lower the pressure.
After receiving a further order from our customer, we gave the go ahead to our engineer to use his refrigerant recovery unit to decant the gas. The refrigerant is sucked into the unit using a small one cylinder reciprocating compressor. The compressor discharges into the on board condenser which is cooled by a fan. The subcooled refrigerant travels down a refrigerant hose which is connected to the recovery cylinder in the picture. After this process was complete, he started looking for a leak...
The leak was identified on the flange for the expansion valve. This component was removed, cleaned with our in house refrigerant grade solvent, then the joint re made with a compound suitable for the temperature range of the component. After a satisfactory nitrogen pressure test, the evacuation process can begin…
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Each of our engineers carry a high capacity vacuum pump of the highest quality. We believe in investing in state of the art equipment as this is part of how we provide the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. Good equipment makes the job go easy.
The pump works by sucking vapour into the inlet port. A rotary vane system extracts the vapour and discharges it through the top of the pump module. Oil is used to lubricate the vanes that slide around the pump cylinder. The vanes are kept a tight fit against the cylinder with the use of springs. As our pumps are high capacity, an oil filter is fitted to the outlet with a gauze inside to catch any oil droplets.
This motor fits onto the back of the vane pump module. It comes from the factory set to 240v, but we change the pins for the electrical connections to convert it for use with 110v. This is because customers and engineers demand the use of 110v as if is safer for use in the UK climate. The 110v plugs and extension cable are shrouded and weather resistant. Weather resistant does not mean weatherproof, so we take measures to limit the exposure to adverse weather conditions. The pump motor, however, is not weather resistant at all, so care is taken to locate it somewhere dry. After a long time running, the motor runs hot, so our engineers take readings and carry out adjustments to ensure that it stays within its nominal operating temperature range.
The vac pump oil is changed before each use with our specialist grade, high quality oil. Contact our office for prices and delivery times. The manufacturer of the pump recommends these oil changes as moisture and impurities absorb into the oil and so reduce its performance, also the working like of the pump.
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Having set up the vacuum pump, our engineer started the evacuation process.
We use analogue Torr gauges as they are more reliable than digital ones. Also, they do not need batteries and it does not matter if they get wet. He attached the Torr gauge to a suitable part of the system with a refrigerant hose, ensuring that a good seal was made between the components with a sealing compound.
Fittings were used to get between the different thread types from the vac pump to the fridge system. Having warmed up the pump for half an hour he was ready to start the process.
One purpose of evacuation is to remove the gasses that will not condense such as nitrogen remaining in the system from pressure testing. Another non condensable is air that has entered the system from when the expansion valve was removed. These non condensables affect how a fridge system works according to Dalton’s Law of Partial Pressures: that all gasses in a vessel act as if they are on their own. The non condensables cause a higher head pressure and false readings: when this pressure is added into our calculation- it throws out the sum and so gives a false reading of subcooling.
The other purpose of evacuation is to dehydrate the system. Water, as we know, has a boiling point of 100°c at sea level, which is 1bar absolute or 760 Torr. As you start to drop the pressure, so correspondingly, the boiling point also drops. For example, water boils at the top of Mount Everest at around 68°c. If we continue vacuuming a refrigerant system, eventually we can remove all moisture by dropping the pressure below the saturation point of water. This works even in the winter in UK ambient conditions. Moisture in the system causes system failures and malfunctions leading to expensive breakdowns.
To read more about flow switches hit the Tag at the top of the page.
Chilling Plant Service
Read more about rotary vane pumps at Wikipedia | Click Here
One of the most important parts of a chiller maintenance company is the diagnosis. If this is done wrong, the wrong parts are ordered and the return job goes wrong.
News Article No.7
For us at Maximus Chillers, it is imperative that we get the diagnosis right, so the return job goes easy. On a maintenance visit, a detailed Tick Sheet is completed with all the necessary readings and adjustments.
One of our engineers was on a maintenance visit recently and he found an electrical fault with a relay. An intermittent fault- so the most annoying to diagnose. The relay interlocks the compressor A1 run signal on the start contactor. The fault causing the relay to drop out was the high pressure condition. The high pressure switch was found to be in good working order with continuity back to the relay, so the relay was deemed to be not switching intermittently. The relay was changed with the available stock on site and the machine went back into seamless operation.
At Maximus Chillers we know that incorrect test equipment can lead to incorrect diagnosis. That’s why we have the highest quality equipment which is regularly inspected, replaced or calibrated. With a Fluke multimeter with fused leads- we diagnose the most complicated of problems. Sometimes a wiring diagram is not available, or the machine has been modified. Even wires disappearing into a conduit and ending up on the other end of the chiller can be traced and effectively diagnosed. You can rest assured that with the ongoing maintenance by Maximus Chillers- we will extend the useful life of any chiller.
For over the phone diagnosis, our contract customers enjoy the full benefit of our technical support desk. Faults are often something and nothing, or are just to do with how the machine was restarted. If we can get a chiller away over the phone, that saves us time and that saves you: the customer money too. Just part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere.
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We at Maximus Chillers have a comprehensive range of expansion valves, on the shelf, in our stores at our chiller maintenance company in Droylsden, Manchester. There are three commonly used types of expansion valve used on a chiller:
This is a simple design of a solenoid coil lifting a solenoid valve and opening the diaphragm in the expansion valve. This allows the refrigerant to pass from the high side of the system into the low side. A sensor either side of the evaporator feeds back to the controls. The controls work out the length of time the valve stays open and the length of time the valve stays closed. Quite a simple idea and quite reliable from our experience too. The replacement of parts are a straight swap.
Another type of valve we stock is the electronic expansion valve. Similar to the above, this valve uses a sensor either side of the evaporator to work out the superheat. Another method of working out the superheat is a sensor and a transducer. Either way amounts to the same thing: the controls work out the difference in temperature and saturation point. The mechanical part of the valve is a step motor which winds all the way shut when the chiller starts. This is so that the controls can register step 0. As the valve opens, the controls record the amount of steps and so opens and closes for a close control of the superheat.
A thermostatic expansion valve is a completely mechanical and stand alone part. The pressure in the bulb increases with temperature and so forces the valve open. We have the full range of orifices for the commonly used varieties of valve on the shelf. Each orifice is used for a different application, ranging from low temperature -40° saturation, through medium temperature 0° saturation, to high temperature 20° saturation. High temperature applications include laser chillers- the secondary refrigerant cools the oscillator and the laser head.
HFC refrigerant is being phased down to 21% by 2030. This is in accordance with F-gas guidelines and the emission reduction measures as defined in the Kyoto Protocol. This refrigerant, however, still remains to be the most popular type amongst chillers, with new chillers coming of the production line charged with, most commonly, R407c and sometimes R410a. R134a is also a popular chiller refrigerant most commonly used in flooded centrifugal chillers. The more the phasedown starts to pinch, the more the incentive to use a lower GWP (global warming potential) drop in refrigerant. This extends the useful life of the chiller, therefore removing the need to build a new chiller, with the associated high amount of carbon emissions.
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At periodic intervals according to the maintenance schedule, the end plates are taken off the chiller evaporators and the tubes are inspected. We have calibrated eddy current instrumentation to assess the integrity of the evaporator tubing. This equipment uses electromagnetic coils to produce eddy currents, the electrical impedance is then measured. It picks up any cracks, pitting or corrosion. The conclusions are mapped onto a chart showing the tubes which are likely to fail. These tubes can be taken out of operation to prevent catastrophic system failure in the future. The system can then be pressure tested in accordance with F-gas leak testing requirements to prove the integrity of the system. Just part of the joined up forward thinking of this chiller maintenance company.
On our maintenance visits, one of a long list of checks is to check the insulation and vapour seal. If the lagging is not in place correctly, moisture from the air forms as condensation on the steel shell. This is not visible, so the condition of the steel can deteriorate dramatically over time. Where the lagging is in good condition, industry guidance states that it should not be removed to inspect. Where the lagging is in poor condition, however, it should be stripped back to the location of a good seal to inspect the integrity of the shell. For low temperature glycol or brine applications, rapid deterioration occurs as the shell is defrosting and re freezing between production cycles or defrost cycles. We heat treat the steel to remove all the moisture, then grind off any rust, before adding a two kinds of specialist paint available for sale at Maximus Chillers. We then match into the old lagging for a good join with our off the shelf varieties of lagging. The lower the temperature of the application, the greater the thickness of the lagging supplied.
Air Cooled Chiller Planned Maintenance
To read more about chiller diagnosis hit the Tag at the top of the page.
For further reading on F-gas enforcement reforms visit RAC Magazine | Click Here
A nice day to carry out air cooled chiller maintenance at a new site we have taken over in the South East.
News Article No.6
Our engineer attended site at around 9am with the risk assessment method statement having been sent in advance. A site survey was carried out to see if there were any additional risks. Should there have been any changes- the RAMS have a section for the additional risks and control measures. After gaining a permit to work, our engineer was issued with a security pass to access the chiller compound. Three chillers are located in the compound which feed air handlers for a critical application. Two of the chillers are multiple system, scroll compressor, air cooled chillers. The other is a single system screw chiller.
A complete download of the program settings is available in our engineer’s phone. This is to cross reference the settings, should one of them be accidentally changed by the maintenance engineers. Onsite engineers are the first port of call for chiller trip outs, with the responsibility to get the plant up and running. We offer real time assistance, over the phone from our Technical Support Desk and can send user manuals in PDF form, direct to their computer. The settings were found to be nominal, so a detailed analysis of the alarm history was carried out:
In reverse date order, the alarm history of all the systems was interrogated. There had been several system shut downs to carry out the periodic maintenance by the onsite personnel. The electricity having been shut down, there was a subsequent oil pre heating timer in the history too. On Chiller 2, System 1 however, there had been several low pressure trip outs. Our engineer decided to start the maintenance with this system by carrying out a full diagnosis of the low side of the refrigerant system:
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The system runs on R410a refrigerant. This refrigerant has higher operating pressures in comparison with other HFC refrigerants. It has an efficient temperature range which can be seen on a pressure enthalpy chart. Below or above this range- the refrigerant loses efficiency and so has a lower coefficient of performance. The most common saturation point for this refrigerant is 0° which corresponds to a 7 bar suction pressure in the evaporator. Above this is the superheat of the refrigerant returning to the compressor. On this occasion there was found to be 26° of superheat and a suction pressure of 4 bar- close to the low pressure trip out. After careful diagnosis, our engineer decided to focus his attention on the expansion valve:
There are 4 forces acting on a TEV:
Liquid line pressure coming from the condenser.
Suction pressure down the equalising line from the far side of the evaporator. This compensates for the pressure drop across the evaporator and shows the true compressor side pressure.
Spring pressure acting upwards and closing the valve.
Bulb pressure forcing the valve open.
To reduce the superheat, the bulb should have forced the valve open. The refrigerant charge in the bulb acts upon the bellows to achieve this. The reason for the malfunction, on this occasion, was found to be the failure of the expansion valve orifice. It had become jammed- causing a shortage of refrigerant in the evaporator/ high superheat.
Our engineer was carrying out the above fault finding with one compressor running and the other two being held off. This was to prevent a low pressure trip. Where chillers are left running with a high superheat condition, the reduced amount of latent heat causes a higher cost in electricity relative to refrigeration effect (COP) The refrigerant carries on superheating without absorbing latent heat- pointless and inefficient for a chiller.
For convenience, this chiller can be pumped down and valved off using the service valves. The evaporator can be worked on after breaking in procedures are carried out. Therefore, we have arranged for this to be carried out before fitting the new expansion valve parts. These chillers also have the ability to pump down the refrigerant on receiving a fault feedback from the electronic leak detector. This is an added measure to lower the environmental impact of refrigerant leaks.
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Cooling the refrigerant vapour down, through the latent heat phase and then subcooling the liquid down further. On System 2 of the same chiller, a subcooling issue was identified. 21 bar/ 36° saturation was normal for that system as defined by the fan speed controller. Now, the system pressure was higher at 28 bar/ 47° saturation, so our engineer decided to work out the subcooling. A very high reading of subcooling was recorded at 28° this was diagnosed to be due to non condensables in the refrigerant:
Non condensables are gases that will not condense, such as, air and nitrogen. If nitrogen is not vented properly and a deep vacuum then achieved, the gasses will remain in the refrigerant system. When calculating the subcooling, the readings work out incorrectly due the presence of the gasses. This can lead to false diagnosis. The remedy for the issue was to arrange a full refrigerant decant, pressure testing and dehydration, before charging with new refrigerant.
Having good subcooling values on a refrigerant system is critical to efficiency. Where there is no subcooling- the refrigerant has not fully rejected all the latent heat from the condenser. This can be seen when looking at a PH chart and plotting the pressures and temperatures. This heat remains in the refrigerant and adds to the system along with heat added from the compressor and heat from the process. This is another reason the coefficient of performance is reduced and so incurring increasing electricity costs for the plant.
These chillers are also fitted with refrigerant economizers- one for each system. They work by diverting some of the refrigerant from the condenser, through a small expansion valve, then through a plate heat exchanger. The rest of the liquid refrigerant passes on the other side of the plate heat exchanger and so is further subcooled.
Air Cooled Chiller Planned Maintenance
To read more about air cooled chiller maintenance hit the Tag at the top of the page.
For further reading on chilled water visit Wikipedia | Click Here
The chiller maintenance schedule in essence is as follows:
News Article No.5
N+1 is intrinsic in the development of a chiller maintenance schedule. N+1 means the amount of cooling required + the same amount again in parallel. It can also be represented as 2N. Two water system pumps are a good example: where the pipework splits in two- one pipe for each pump. When a pump fails, the redundant pump comes online. Chillers are arranged in parallel, in this way, on the water system. This redundancy allows for a stress free maintenance of the plant. The failed system can be rectified and brought back online while the redundant system takes the load.
The intervals in the contract are influenced by the redundancy of the chillers on site. The less run hours the compressor does, the less maintenance is required. We at Maximus Chillers can tailor make a maintenance schedule exactly to your needs by looking at how much the chillers are used and how hard they work.
For some applications, the chiller operates under a high load condition all the time, with a redundant system in standby. On other applications, the chiller works in minimal load conditions. Regardless of the load conditions, the chiller is critical to the cooling of buildings or for an industrial process.
An important thing to remember is to balance compressor run hours and bearing wear by rotating the lead/ lag duty of the chillers. This can usually be done in the in the sequencer (if fitted) by changing a program setting. Otherwise, the switchover controls can be changed on the off/hand/run toggle switches. Where manual changeover is required, the onsite engineers are usually conversant with the procedure concerning the water system pumps, valves and controls. During the maintenance, the stop checks can be carried out on the redundant system, while the run checks are carried out on the system which is online.
Reciprocating compressors require a log of the compressor run hours. This is because the valves and bearings should be changed at pre prescribed intervals as laid down by the maintenance schedule. Particularly important to reciprocating compressors are regular oil changes and oil sampling- a small change in the result of an oil sample can prevent a serious compressor smash up. A check list including the model number and serial number is completed on each visit and kept in a file on site. This file can be consulted during diagnosis and maintenance to decide on the beast way forward with an on going issue.
Air cooled chiller condensers can often be looked after by the onsite engineers in between maintenance visits. Just a quick brush down every few months is usually all it takes. Where the environment lends to a type of contaminant being collected on the condenser coils, an effective chemical is selected from our stores and used on the coil. Where there is an issue with the serviceability of the condenser, we can put together a plan to keep on top of it. We can even retrofit a new condenser- it’s what we at Maximus Chillers call the MAXIMUS ADVANTAGE™
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The shell is made from a heavy steel sheet rolled into a circle. The seam is welded together to form a cylinder. The tubes are pushed though the tube holders which are made from steel and are welded into the shell of the evaporator. The tubes are copper because of its good thermodynamic properties.
Direct expansion is achieved in an evaporator with a thermostatic, or electronic expansion valve. The refrigerant enters the valve from the condenser as a high pressure, hot liquid. The pressure drop on the evaporator side of the valve makes the refrigerant flash off into a cold, saturation point liquid and vapour mix. The liquid boils off, absorbing latent heat through the inside of the copper tubes. On the outside of the copper tubes is the return water from the process, or the cooling of buildings.
The parts of the maintenance schedule that relate to DX evaporators are:
The inside of the tubes are in the clean environment of the fridge system. This means they do not become fouled. A tube insulating issue can be caused on the inside by oil. If there are issues with the oil return system, the oil can pool in the evaporator. A low refrigerant charge can have the same effect. Written into the maintenance schedule are manual oil return and oil draining visits. During these visits, the monitoring of the refrigerant charge is also carried out.
If a sensor is not located in its pocket correctly, or without sufficient heat transfer paste- it will read incorrectly back to the electronic expansion valve driver. This will cause the expansion valve to malfunction.
A full maintenance of the pressurisation unit is carried out. This includes the pumps, controls and program adjustments as required. Incorrect pressure in the water system will cause a knock on effect of faults on the chillers.
As above with chiller lead/ lag change over, water system pumps are manually changed over from lead to lag in the building controls. Carrying out this procedure reduces the chance of pump failure between visits. This is because it balances the pump run hours and so prevents bearing seizure after a long period not running.
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Flooded evaporators are the reverse of the above DX evaporators. The refrigerant is on the outside of the tubes, with water on the inside of the tubes. Gravity and refrigerant charge determine the refrigerant level in the condenser and evaporator. In between the two is located the liquid pipe with the orifice located in the pipe for the expansion of the refrigerant. The cooling water flows through the condenser tubes and off to the cooling towers. On the low side, the chilled water flows through the evaporator tubes and off to the process, or the cooling of facilities.
The parts of the maintenance schedule that relate to flooded evaporators are:
Because the condenser cooling water and chilled water systems are pumped through the pipes, the tubes become dirty over time. This occurs more often on the condenser as the water towers are open to atmosphere. Contaminants from surrounding buildings and factories gets into the water system and thermally insulates the tubes. This thermal insulation reduces the heat exchange through the copper tubes. The knock on effect is higher head pressures and eventually high pressure trip outs.
We at Maximus Chillers have in our stores the required equipment to carry out the cleaning of the tubes. Our engineers can attend site and liaise with the onsite engineers as regards the draining, strip down and lift out of the heat exchanger end plates.
A water sample is taken from the cooling and chilled water systems. These samples are sent off to our laboratory for analysis. Bacteria can build up in the water system causing slime- this can be rectified with a careful selection of chemical agents. Also, silt can build up- various chemicals are added to positively charge the silt and so carry it around the system to the strainer. Where the issue is caused by rust- an inhibitor can be added to prevent, or slow the oxidization of the steel.
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The frequency of F-gas leak testing is determined by the size of the plant. This will be detailed in your F-gas file which is kept on site. Another record of this is kept by the chiller company at their registered office. The copies of the periodic leak testing sheets are kept by both parties. These detail the result of the test, refrigerant added to the system, refrigerant removed from the system and the required follow up actions. Some methods of leak detection are:
On each visit our engineers remove the coverings of the ends of the condensers and panels. This is to inspect the whole machine for a sign of a leak. Any potential leak is marked for future identification of the location. A visual inspection will always be backed up with a further diagnosis such as:
These readings are taken during a maintenance visit to determine the refrigerant charge of the chillers. The engineer, however, has to bear in mind that the subcooling and superheat readings can read abnormally due other reasons.
Various makes are available from the suppliers. Each engineer having his own preference. We at Maximus Chillers stock leak sprays and a wide selection of other materials.
This type of leak detector is installed in the chiller low down in the panel. This is because HFC refrigerant is heavier than air. The leaking refrigerant will tend to pool in the bottom of the various panels around the chiller.
Each of our engineers carries a portable sniff tester. It comes with an extended tip to get into the most tight and awkward places. The leak detector has a replaceable element inside the unit. It also comes with replaceable tips which can be swapped out periodically. They come with a portable plug socket and transformer to charge the on board batteries after use in the field.
Air Cooled Chiller Planned Maintenance
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Chiller compressors fail often the result of ineffective servicing and system testing.
News Article No.4
At Maximus Chillers, we carry out extensive tests during our visits to ensure that small problems are resolved before they become big problems. If we notice a reading starting to become abnormal, we can carry out the diagnosis, then do the necessary service. Some of the compressor readings we monitor:
The suction, discharge, motor windings and bearing temperatures are recorded for comparison to previous visits. These are often available in the PLC for the chiller, or our engineer can take the readings with his test equipment. Problems with the oil system can be the cause of higher compressor temperatures, the system running outside of its nominal operating conditions is another reason. Magnetic drive systems have an advantage as they do not use oil.
Portable vibration sensors are carried in of each of our company vehicles. This is an accelerometer to measure vibration. Along with other system readings, we keep an on going record of the vibration levels around the compressor. When internal components are coming out of alignment due to wear, this causes an out of balance condition in the compressor. This, in turn, causes a knock on effect- causing other components to go out of balance. Catching this condition early will prevent a compressor smash up resulting in the replacement of expensive internal components.
Another way of preventing big problems to occur is periodic compressor oil testing. Samples are taken, usually on alternate visits, which are sent off to a laboratory for analysis. The acid level is tested to provide pre warning of a potential compressor motor windings burn out. This is because acid in the compressor oil rots through the electrical insulation on the motor windings. The presence and quantity of white metal and yellow metal is analysed too. This is a window through to a component starting to wear inside the compressor.
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The compressor in the photo is a screw compressor. It operates with ammonia refrigerant. This refrigerant is usually used for low temperature applications, mainly associated with food production. This compressor, however, has a 1° refrigerant saturation and is used to cool computer rooms. Common causes of compressor failure on this kind of compressor are:
The various compressor components are sealed together using ‘o’ rings or paper gaskets. ‘O’ rings are especially prone to leaks due to work hardening and flattening of the sealing face of the ‘o’ ring. The system can be pumped down and the compressor valved off. Then, our lift and shift team can remove the compressor to our remanufacturing facility for strip down.
The mating surface of a shaft seal has a mirror smooth finish. This is to reduce friction and aid with a better seal. Over time, this starts to wear, causing an ineffective seal and a leak of refrigerant and oil. A service visit can be arranged to change the shaft seal on site. The shaft couplings can be split, the shaft seal can then be removed and replaced. A quick job, then the machine is up and running again.
This is an electronic device with a slide attached to the moving compressor slide valve. The device has a start and an end position programmed into it during commissioning. The potentiometer converts the slide valve position, usually into a 4-20mA signal which is fed back to the chiller PLC. They are prone to reading out or the reading being jammed in one position. This results in a trip out from the controls, as the controller is not able to determine the true position of the compressor slide valve. We have an off the shelf stock of slide valve potentiometers for the various compressor range. A service visit can be arranged to replace the part after diagnosis has been carried out.
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Centrifugal compressors are a very reliable kind of compressor but when they go wrong, they can go wrong in a big way. Compressor overhaul is expensive, this can be carried out onsite, or a better option is a lift and shift to our remanufacturing facility. Proximity sensors are usually fitted to monitor the distance between the impeller and the casting. This is an added protection along with the other sensors and transducers around the compressor.
We are on account with Micro Control Systems- an American company who specialise in building panels to order for specific chiller compressors. We easily fit this control system to any compressor to control the loading of the vanes in accordance to the available load from the process. The control panel has previously been fitted to other machines of the same model number, so any teething issues have already been ironed out. Maximus Chillers can achieve seamless operation of your plant.
Newer centrifugal compressors are oil free so as to eliminate any of the service issues relating to oil. There are a substantial amount of compressors, however, that use oil to lubricate the bearings. This kind of compressor, if properly serviced, can last for 50 years. The oil system picks up impurities which are caught by various filters. These filters can be changed or cleaned according to the prescribed service schedule. Our engineers make sure that spares are ordered and kept onsite prior to a visit.
Our visits and ongoing upkeep of your plant saves money. Money spent as a preventative measure saves so much more money in the long run. With competitive prices on specialist internal compressor parts- Maximus Chillers completes the picture. When compressor failure occurs, you are in safe hands with years of industry experience invested in each of our engineers.
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With high discharge pressure, there is a corresponding increase in discharge temperature. This means that the compressor is operating beyond its recommended values. The cause of this is often a poorly maintained condenser. Especially on industrial chillers, there can have been gaps in the schedule where the condenser was not correctly serviced. This condition is often rectified easily by an onsite engineer by giving it a brush down. Where the fins are bent over- we carry a specialist tool to straighten them back out- how they came out of the factory. We also use different formulas of chemicals to rinse the various kinds of dirt from deep within the fins.
Some chillers are used where very high water temperature can come back from the process if the chiller were to be off line for a short period. Usually, this happens in factories where certain industrial processes are being carried out. When the onsite engineers start the plant back up, the chiller experiences a high heat load to deal with.
Maximum operating pressure expansion valves limit the pressure in the evaporator to a given level, regardless of the available heat load from the process. They do this by having a limited amount of liquid refrigerant in the bulb. When this runs out, the power element cannot push the orifice open any further- thus limiting the suction pressure. This is important to prevent scroll compressor failure as it prevents putting added strain on the compressor motor windings due to high suction pressure.
Where there is a shortage in refrigerant, there follows a low oil level condition. The refrigerant mass flow rate, carries the oil around the system and back to the compressor. This is greatly impaired when the chiller is short of gas. The oil cools the compressor and lubricates the shaft bearings. These bearings and other internal components wear down and seize causing failure. Maximus Chillers can put together a package to minimise chiller compressor failure.
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A chiller service company can carry out diagnosis even when a wiring diagram is not available- our engineers can trace the wiring around the chiller.
News Article No.3
This often aids with diagnosis even when there is a wiring diagram, as to have your eyes on a component often makes more sense than a symbol. In any case, our engineers carry out system testing with Fluke multimetes and ammeters. We carry a range of thermocouples and probes to be used in conjunction with our calibrated digital thermometers. We use these along with comparators to carry out leak testing…
According to the frequency dictated by the quantity of refrigerant, we use the above test equipment to carry out F-gas leak testing. First, we have a visual look around the chiller for a sign of a gas leak. All parts of the pipework and system components are inspected. Then, we carry out a full refrigerant diagnosis to determine that the refrigerant system is operating with a full charge of refrigerant. The report for each chiller being completed and filed in the onsite F-gas leak register. A history can be built up to assess the serviceability of the plant and the frequency of leaks.
Where intermittent faults are concerned, on going system monitoring is required. If the job is not progressed on each visit, there is little point in a call out. We carry out tests during monitoring and ensure that the wiring is tight. Hopefully, waiting for the fault to occur whilst next to the machine. Alongside this, we rely on a report from the end user, as regards, the symptoms and the circumstances of the chiller when the fault occurred. From this we extrapolate the diagnosis and decide the next step to take. This may be to attempt to move the fault to another machine or, at least eliminate one thing each visit.
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These have a rolled steel shell, welded down the seam with and end plate on either end. The water system pipes can be bolted to the sides or the end. The endplate can be removed for access to the waterside of the tubes. A strainer is fitted to the inlet to catch any foreign objects that may have been carried around the water system. Inlet and outlet gauges are fitted for the monitoring of the water system readings during a service visit. On larger chillers the screw or centrifugal compressor is mounted directly on top of the evaporator- sucking directly off the top of a flooded evaporator…
This kind of evaporator has the refrigerant in liquid form on the outside of the tubes. These are a rack of copper tubes extending through the length of the shell. The warmer process water running through the tubes causes the refrigerant to boil off. A sight glass is usually available to check the state of the refrigerant evaporating on the copper tubes. The suction from the top of the evaporator goes round a baffle so as to prevent the slug back of liquid refrigerant into the compressor. The refrigerant flow into the evaporator is controlled by the expansion valve…
This takes the form of a fixed size orifice on the liquid line in between the shell and tube condenser and the flooded evaporator. The size of the orifice previously being calculated to match the mass flow rate of the refrigerant dictated by the compressor. Some newer systems have a variable orifice for the more efficient running of the plant. This is controlled electronically along with the loading of the compressor, relative to the available load condition.
Smaller DX evaporators are usually multi system. This gives an N+1 redundancy of the plant. Indeed, when one side of a 2 system evaporator is having service work carried out, the other side continues to operate normally. Thinking ahead and allowing for additional capacity is essential when the application is critical, such as, a data centre or a hospital. When a redundant system comes online due to a failure- getting the system back up and running is a matter of urgency. For this we offer same day delivery of parts and a fully stocked mobile workshop.
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Various configurations are employed to ensure good air flow through the chiller condenser fins. The most popular being a ‘v’ condenser as the surface area is increased with this design. Powerful fans are used to reject the air and heat upwards and away from the chiller. Where system location causes the recirculation of air, duct work can be fitted to direct the air away from the chiller.
A popular kind of pressure transducer used on condensers is Johnson Controls. These can be bolted onto the refrigerant discharge pipe to sense the system pressure. They have a 5vdc input that comes into the transducer on a red wire, a black wire is the ground and a white wire is the signal back to the fan speed controller. The transducer has a minimum to maximum range, so a chart can be used to determine if the signal is reading back correctly. On chillers where the transducer is wired directly in the controller- calibration can be carried out to offset the readings.
Another kind of pressure transducer is the 4-20mA type. It sends a mA signal back to the controller or the fan speed controller. 4mA is the minimum position, so this relates to the minimum of the transducer pressure range.
R134a refrigerant operates at a lower pressure in a condenser than the other commonly used HFC refrigerants. If you were looking for a chilled water set point of 6° in the UK ambient for example, the R134a refrigerant saturation on the high side of the system would be around 36° Latent heat from the water system and heat added into the refrigerant from the compressor are rejected from the condenser. As the refrigerant passes down the condenser tubes, cool air blowing across the outside of the tubes, cools the refrigerant vapour down through the latent heat phase and into a subcooled liquid.
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This kind of compressor has a lower volumetric efficiency compared with the positive displacement compressors below. This is because the refrigerant is compressed using centrifugal force off the tip of the impeller, instead of being mechanically compressed. The advantage of this kind of compressor is a high mass flow rate of refrigerant. These compressors are used in factories where a large amount of chilled water is required to cool the process. They are also used in countries where district cooling is used. The chillers are arranged in rows in a chiller hall and are piped into the district cooling loop.
Oil used to lubricate the bearings is also used to create a seal between the rotors. Computer aided design (CAD) software and computer numerical control (CNC) grinding machines are used in the construction of screw rotors. The shape of the rotors is designed to compress the refrigerant along the screw. The length of the screw that is available to compress the refrigerant can be adjusted with a slide valve. Any stage of loading between 0- 100% can be achieved. This is regulated with a slide valve potentiometer. Screw compressors are very reliable and have a long service life. They also have a low vibration reading which ensures a lower instance of refrigerant leaks around the compressor.
A service free compressor. Service free assuming that the rest of the system is functioning correctly. This kind of compressor relies on oil migration around the system. The oil is entrained along the inside of the pipework, around the system and back to the compressor. An oil level sight glass is fitted into the body of the compressor at the required level. Refrigerant shortage can cause the oil to stay in the bottom of the evaporator, causing a low oil level condition in the compressor. Chiller service companies can be scheduled to attend site to drain the oil, then pump new oil into the compressor.
When any of the above compressors fail, you are in safe hands with Maximus Chillers. We have the capability to lift and shift the compressor to our remanufacturing facility for a full overhaul. The reason for the failure is diagnosed to ensure the new compressor does not fail for the same reason. Improving the reliability of your plant and extending its life is what we are all about- if we can reduce your service costs- that makes us happy! All temperatures and pressures are recorded to ensure the replacement compressor goes into seamless operation.
Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere- The MAXIMUS ADVANTAGE™
Chilling Plant Service
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Featuring planned preventative chiller maintenance- in a series of longer, in depth news articles:
News Article No.2
This time concentrating on the checks, adjustments and diagnosis our engineer carries out while on site. We can extend the life of your plant and reduce energy costs- just with the effect of our maintenance. As well as completing a detailed checklist which is sent in to your office in PDF form, our engineer carries out extensive F-gas leak testing.
The first part of the maintenance is carried out to the controls of the redundant systems. This is because all the pressures and temperatures should be reading the same. If not, this is an opportunity for:
Before calibrating a sensor that is reading out, our engineer carries out a diagnosis to assess the serviceability of the sensor. With NTP (negative temperature coefficient) and PTC (positive temperature coefficient) sensors, the resistance is taken at a given temperature, which is then compared with a chart. With pressure transducers the 0-5vdc feedback signal is analysed to see if it is within the allowable tolerance. Once this diagnosis is complete and the sensor is deemed to be in good working order, our engineer will then calibrate the sensor. A password is entered into the PLC (programmable logic controller) to gain access to the service menu. From here, he can select the particular sensor, then offset it by the required amount. A lot of controls are not linear, that is to say, a sensor reading 2° high being reduced by 2° may not calibrate correctly. An amount of trial and error is often required, also the monitoring of the sensor against a digital thermometer at various temperatures.
Each program setting and timer in the various menu levels is checked against the previous maintenance checklist. Sometimes these are changed accidentally by the onsite engineer when looking for something else- it is easily done.
Each component on the safety chain is manually tripped or the fault condition is replicated to cause the device to trip. This part of the PPM (planned preventative maintenance) is essential to ensure the safety chain protects the chiller during a fault condition. Compressor failure or evaporator freeze up can occur with dramatic cost implications. We routinely prevent small problems, such as a faulty switch, becoming big problems.
Each wire on the chiller is checked for tightness including the fans (on air cooled chillers) the compressor motor connectors and compressor contactor contacts. Loose line wiring will cause breaker and fuse faults. Loose control wiring will cause error messages and chiller faults. This is a call out in between visits that can be eliminated. With the effect of our maintenance, any chiller becomes more reliable and has lower energy costs.
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After the above stop checks are carried out, system run checks are carried out:
Using R134a refrigerant as an example, the refrigerant pressure will be 1.9 bar at 0° This refrigerant is in the HFC (hydrofluorocarbon) family- a commonly used refrigerant. If the refrigerant vapour returning to the compressor is excessively superheated- this is a sign of system issues. Here are some of the causes for a high superheat condition:
Not enough latent heat being absorbed by the refrigerant in the evaporator. This allows the refrigerant to carry on superheating with the available heat load. Refrigerant leak testing is required to identify any leaks. The history of maintenance checklists can be consulted to see if the issue had been deteriorating over several maintenance visits.
A thermostatic expansion valve operates with a higher superheat value, whereby an electronic expansion valve has a much closer control. In either case, our engineer will be accustomed to the nominal readings.
This type of valve is operated with a power element and orifice. A bulb is clamped onto the suction pipe which is connected to the power element via a capillary tube. The power element is pressurised with the same refrigerant as in the chiller. Some of this refrigerant is in its liquid phase, so with an increase in temperature, there is a corresponding increase in pressure. This pressure acts against the diaphragm and so pushes the orifice open. The orifice allows more refrigerant through the valve. When load conditions change and there is a reduction in heat load, the reverse happens- the orifice closes and reduces the amount of refrigerant through the valve. When the power element looses its charge- the orifice shuts down causing a high superheat condition. A low pressure trip out can also occur.
This type of valve uses sensors on the liquid and vapour sides of the evaporator, or a transducer and sensor vapour side of the evaporator. This is so the program can work out the superheat value. If the sensors are faulty, the valve will not operate correctly and a high superheat condition may occur. If the step motor or driver have failed- replacement parts are required.
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This is the measurement of the refrigerant condition in the condenser. Air cooled condensers are particularly popular in the UK as the ambient conditions make them very efficient. Shell and tube condensers are used on lager systems- these are cooled down using a water tower. When there is a refrigerant shortage, the liquid does not stay in the condenser long enough for it to subcool sufficiently. Some of the refrigerant stays in its vapour phase. With not enough latent being rejected in the condenser- the chiller’s COP (coefficient of performance) will be reduced. This means high energy consumption relative to the refrigeration effect of the chiller. This condition can be remedied with a scheduled visit from one of our team.
Air Cooled Chiller Planned Maintenance
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Introducing a series of in depth news articles, this time featuring the chiller maintenance checklist:
News Article No.1
This article has been written with you- the customer in mind. Read below for practical advice on how to keep your chillers in the best condition.
Each day when you walk round, you can check to see if your plant is starting to malfunction. Become accustomed with the usual readings to help you diagnose the faults.
Here are the things to check for and how to remedy them:
Keep an eye on the pressure in the water system.
On a small chiller, there will be a water outlet pressure gauge. Make a mark on the gauge where the pressure is when the chiller is in good working order. You can use this mark to notice if the pressure is starting to drop off.
The most common cause for low water system pressure is a blocked strainer. It is usually a ‘Y’ type with a bolted fitting. With the chiller off and the water system valves closed, unscrew it and check for debris. If it is blocked, make a note of how long it took to block, then add the cleaning of the strainer into the periodic maintenance schedule.
Ensure the pump rotation is correct by checking that the cooling fan is sucking into the pump. If it is going backwards: isolate electrically, then swap any 2 of the 3 phase wires. Brush down the inlet to the cooling fan to ensure good air flow and a cool pump motor.
On a large chiller, the water system pressures may be available in the controller- have a look through the menus. The pressure will be measured in bar. Another popular method on a large chiller is a flow meter. This may be a stand alone device on the chiller panel, or on a control panel nearby. It will read in m3/hr. Check to see if the pressure or flow is lower than usual. If so, ring one of our trained professionals.
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The chiller should be:
In any case, you will become accustomed with the usual chilled water temperature according to varying load conditions. If the plant is struggling to achieve set point, or is running higher than usual- this is a sign of system faults.
Walk along the chillers that feed the same water system and make a log of the faults showing on the controllers.
Here are the things to check for high water system temperature:
If it has a low pressure gauge, look to see if the pressure is lower than usual. If so, this is a sign of refrigerant shortage in the plate evaporator. A scheduled visit from one of our trained engineers to carry out a pressure test can be arranged.
Look for any breakers that have tripped in the panel. One reset can be carried out by a qualified onsite electrician. If the fault reoccurs- ring our support team. If the scroll compressor has tripped, check to see if the compressor is hot. If so, isolate and do not attempt a restart.
A blocked condenser will inhibit the rejection of heat. Brush it down and give it a rinse with water. A common occurrence onsite with some condenser designs is a panel being left off with the chiller running! This happens when the onsite engineers are fault finding another issue with the chiller. The fans will suck through the opening as this is the easiest path. The gauge will be higher than usual as the condenser builds in pressure. A high pressure switch trip out will occur.
To locate the switch- first identify the discharge pipe. It is the smaller of the 2 pipes on the compressor. The high pressure switch will either be bolted onto the pipe, or a thin pipe will lead from the discharge to the frame of the chiller. In any case, you are looking for a small box with a button and a wire leading to the panel. Press the button and you should hear it click. If this fault reoccurs- ring our technical support desk.
Should there be a refrigerant shortage, the controller will display a pre alarm: suction limiting. This is the controller preventing the compressor from loading up to prevent a low pressure trip out in the shell and tube evaporator. As above, one of our team of engineers can be sent to site to resolve the issue.
If the controller is showing: discharge limiting- this is a sign of a condenser issue. A full strip down and cleaning of the tubes may be required. Ring our technical support desk for further advice.
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We at maximus chiller can install remote monitoring systems to your chillers so we can fault find and diagnose from a laptop. This means we can give you real time advice over the phone. Now you are accustomed with our chiller maintenance checklist- you can give feedback regarding the plant to assist our engineer.
For our contract maintenance customers: a range of commonly used parts are kept onsite to reduce downtime. We can give practical, step by step advice on the fitting of parts. We often carry out video calls with our customers, as chiller data plates, parts and components can be easier to show than describe.
Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere- The MAXIMUS ADVANTAGE™
To read more about air cooled chiller maintenance click the Tag at the top of the page.
Air Cooled Chiller Planned Maintenance
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