Cooler troubleshooting. In this article, we will examine cooler failures and resolve them. This will cover some of the more common types of failures you may encounter in the industry.
We will cover high discharge pressure, low discharge pressure, low suction line pressure, high suction line pressure, some general electrical problems you may encounter, and some other problems.
Scroll down for the YouTube video tutorial on troubleshooting the chiller
Caveat
Coolers are very expensive and can be very dangerous. So if you are not qualified, competent, or authorized to work there in your or your client's building, don't do it. Instead, seek professional help.
Trick
Something to note: The cooler display unit or BMS units should display an error code if a fault is detected. Write down this code and check with the chiller manufacturer, they should have a maintenance guide that provides information on the cause of the failure.
high pressure relief
High pressure discharge is very common in chillers and is almost always caused by poor water treatment regimes. Make sure your building or your customers' building has a strict water treatment regimen. Especially when you have open cooling towers.
Minerals and dirt will be sucked out of the air into the condenser water loop. This will then circulate through the system and begin to clog the chillers' pipes and heat exchanger. So you essentially start to insulate the internal surfaces of the condenser from the coolers, which will prevent the cooler from being able to transfer its rated heat energy.
A similar scenario occurs with air cooled
chillers where the outer surface of the condenser is covered in dust and dirt. Over time, the air cooler condenser will become covered with a film of dirt. So you want to make sure all tubes and fins are cleaned regularly. But remember that the tubes there are filled with coolant and are very delicate, so be very careful when making them. Use light brushes and also comb fins
Another common problem, especially with air-cooled chillers, is reduced airflow over the condenser and that's usually where some debris has blocked part of the condenser or fans, and therefore not enough air is flowing through the condenser. to take out all the unwanted air. heat away. It could also be that one of the fans has stopped working or is behaving erratically, so you'll want to go up there and visually check that they are clean, unobstructed, and that the fans are running.
High pressure discharge failures can also be caused by reduced water flow through the condenser. First, you should check the valves, filters, and pumps in the systems to make sure they are working and allowing the correct flow through. If you do not have a record of the correct flow rates, locate the systems commissioning data, which should have been given to the building manager when the chillers were installed and tested.
In addition, high-pressure discharge can occur when return condenser water in a water-cooled chiller returns too hot from the cooling tower. Check cooling towers and make sure fans are running, cooling tower bypass valves are properly aligned, and water is not bypassing the cooling tower and back to the chiller.
It could also be due to a partially closed discharge shutoff valve in the cooler. It's a bit unusual for this to happen, but it could have been bumped during maintenance etc.
With air-cooled chillers, it could be that the outside ambient air temperature is above the condenser capacities. So it just can't work under these conditions. You have to wait for it to cool down or adjust the parameters and set points of the chiller. Also, be sure to check with the manufacturer if it is capable of doing this before doing so. One option is to spray water on the condenser, although this will lead to mineral buildup on the fins and the condenser will rest much faster, so this is an option of last resort.
Another fairly common problem that will cause high pressure failures is that the cooler has been overcharged with refrigerant. Walk through the cooler and check all installed pressure, temperature, and sight gauges, as well as BMS readings. It could also be that a non-condensable material or fluid has entered the refrigeration circuit. Check the cooler and listen for noises. If it is caused by foreign matter, then the system will need to be overloaded.
Lastly, if none of these solve the problem, then check the pressure switch for faults!
low pressure discharge
One problem that causes a low pressure discharge is if the suction valve is partially closed, so check for that. It's pretty rare but it can happen.
Insufficient refrigerant charge can cause low pressure discharge. You will need to verify that the system has a sufficient refrigerant charge. If you suspect that this is the problem, it should be recharged.
Another problem could be that the ambient air temperature is simply too low. An air cooler may not work in these conditions and there isn't much you can do about it. You really have to reprogram the system and check with the manufacturers that this is possible. As a last resort, you can heat the air, deliberately cause recirculation, or direct the air taken from the building's ventilation in your direction. Do not use kitchen exhaust air!
The most common low pressure problem will be a dirty or clogged evaporator. So check that nothing is blocking this.
low suction pressure
This may be due to a low refrigerant charge. Check your system for signs of this and reload if necessary. Don't forget to check for leaks as well. If the pressure gets too high in the cooler, it may have vented through the safety relief valves.
One of the most common problems with this will be a stuck regulator. expansion valve.
You should also check the filter drier and strainer. If they are clogged, clean or replace them.
Low suction pressure can also be caused by too low a condenser water temperature. So you'll want to take a look at the set points and design criteria for that. Bypass valves around cooling towers may need to be adjusted to ensure waters return to the correct temperature.
high suction pressure
Now, if you have a high pressure warning in the suction line, there are three main things that could be causing it.
Overloading is probably the main one and this is where the cooling load is too much for the chiller to handle. You want to reduce this if possible. Or extend it to other chillers and cooling equipment.
The expansion valve could overfeed refrigerant. So you want to check that too. If this happens, you may need to replace the expansion valve, but obviously try adjusting the superheat set point first.
The chiller can also be overloaded with refrigerant, so check set points, temperatures, and pressures around the system and then remove (recover) some of the excess refrigerant. This must be done by a qualified specialist.
electrical breakdowns
An unbalanced voltage supply to the chiller can cause failure. You want to measure your voltages on each of your phases to make sure they are balanced. This could indicate that there is a problem with the electrical switch in your building or power quality
A more common problem with chillers is fluctuating voltage or current. This will usually be affected by other equipment connected on the same circuit as the chillers, causing fluctuations or distortion in the voltage and current waveforms. A sudden large inrush to another plant item on the same circuit could trip your chillers.
Another thing will be loose cables or wires. This is more common after a shutdown when a lot of work has been done on the chillers. Maybe some things got unscrewed and didn't fit as well as they should. This can cause the cooler to behave quite erratically. One of the easiest ways to check this is to simply walk around all the connections with a thermal camera and if you see that some screws and connections are hotter than others then you know there is a loose connection there.
Another fairly common cause of this will be a blown fuse or open circuit breaker. Go around and check the low voltage panel fuses and circuit breakers to make sure they were working and not tripped. Check before turning them back on that they are meant to be turned on and that there are no ground faults. Before turning the breakers back on, you must ensure that no one is working on the machine and that the equipment has not been isolated for safety reasons. So talk to your authorized person before doing it.
Another problem, slightly less common but possible, is that you have lost a phase on a three phase supply. Most chillers have three-phase power, but one of the phases may have been lost, broken, or disconnected. The chiller controls should prevent the machine from running in this case.
It could also be that there was a ground fault in the motor and the cooler detected it and shut down. This is more likely to happen on the motor that drives the compressor. You may need a specialist to come and check it out. If there is a power failure, do not try to turn on the cooler. This will destroy the motor.
Another problem is thermal overload of the motor. If the temperature inside the motor housing gets too high, the motor will simply signal and the cooler will shut down to protect itself. You will not be able to turn the chiller back on while this temperature is still above the threshold. This can be caused if the load is excessive or if the motor cooling is blocked or reduced.
The controls
A fairly common cause of error is when flow sensor is breaks, especially the paddleA fairly common cause of error is when the flow sensor fails, especially paddle type sensors. Before turning on a chiller, you need to check that there is enough flow through the evaporator and condenser to prevent freezing. But if the paddle gets stuck, loses communication, or has a fault, it will no longer measure or send the signal to the control unit. The chiller will assume there is no flow or not enough flow and will shut down and not restart until there is enough flow.
Another built-in safety feature is the compressor start time interlock. Chillers will typically only be able to start a certain number of timers per hour. The number of times is defined by the manufacturer to prevent damage from inrush currents. However, if the chiller is oversized and serving a small load (for example, winter load), it may turn off for a period of time and then turn back on when the chilled water temperature reaches the demand set point again. But, it will only be allowed to restart "X" several times per hour. This is to protect yourself and the buildings electrical infrastructure as the inrush current from these chillers can be extremely large.
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