In this article, we will examine and troubleshoot chiller failures.
Caution: On the chiller's display unit or BMS unit, if a fault is detected, an error code should be displayed. Write down this code and contact the chiller manufacturer, they should have a maintenance guide that can provide you with information on the cause of the fault.
High pressure discharge is common in water cooled chillers and is almost always caused by a poor water treatment regime. Make sure that your building or your customer's building has a strict water treatment regime. Especially if you have open cooling towers.
Minerals and dirt will be absorbed from the air and enter the condenser water circuit. This will then travel around the system and start to clog the pipes and the chiller heat exchanger. As a result, it essentially begins to insulate the inner surface of the chiller condenser, which will prevent the chiller from being able to transfer its rated heat energy.
Box Type Water Cooled Scroll Chiller
Another common problem, especially with air-cooled chillers, is reduced airflow over the condenser. This is usually some debris blocking part of the condenser or the fan, so not enough air is flowing through the condenser to take all the unwanted air heat away. It could also be that one of the fans has stopped working or is not behaving properly, so you want to go there and visually check that they are clean, free of obstructions and that the fans are working.
A high pressure discharge failure can also be caused by a reduction in water flow through the condenser. First, you should check the system valves, filters and pumps to make sure they are all working and allowing the correct flow through. If you are not recording the correct flow rate, find the system commissioning data that should have been sent to the building manager when the chiller was installed and tested.
In addition, high pressure discharge may occur when the condenser return water on a water-cooled chiller is too hot when it returns from the cooling tower. Check the cooling tower and make sure the fan is working properly, the cooling tower bypass valve is properly aligned, and that the water is not just bypassing the cooling tower and returning to the chiller.
Air Cooled Screw Chiller
This can also be caused by a partially closed discharge shutoff valve on the cooler. This is rare, but it can get knocked over during maintenance, etc.
For air-cooled chillers, the outside ambient air temperature may be higher than the condenser's capacity. So it simply won't work under those conditions. You must wait for it to cool or adjust the chiller parameters and set points. Also, be sure to confirm with the manufacturer that it is capable of doing so before performing this operation. One option is to spray water on the condenser, although this will cause mineral build-up on the fins and the condenser will stop more quickly, so it is a last resort.
Another fairly common problem that can lead to high pressure failures is overcharging the chiller with refrigerant. Bypass the chiller and check all pressures, temperatures and sight glasses on the installation, as well as the BMS readings. It is also possible that non-condensing material or fluid has entered the refrigerant circuit. Check the chiller and listen for noise. If it is caused by a foreign object, the system needs to be surged.
Finally, if none of this solves the problem, check for a faulty pressure switch!
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