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How To Fix A Chiller System?

Jul. 04, 2022

This article describes how to fix a chiller system that has a compressor stop and low pressure error after start-up.



Low pressure (Lo1 or lo2) error message on the microprocessor controller. After power is applied and the compressor starts, the compressor stops before reaching the SP1 or SP2 set point, the microprocessor displays "Lo 1" or "Lo 2" on the top screen, and the trip pressure and low pressure indicator flickers on the bottom screen.



After the compressor starts, the microprocessor monitors the suction pressure or low pressure side pressure of the refrigeration system. If at any time during the operating cycle the microcontroller finds that the low pressure side pressure is below the LP setpoint for more than 90 seconds, the microcontroller will lock out the chiller compressor until the microcontroller is reset. The microcomputer will then display the above fault and lock out the chiller cooling system.


The micro reset can be done in two ways. First, press and hold the power button for 2-3 seconds. If this does not work, turn off the main power to the chiller for one minute and then turn it back on. If the system starts correctly, a low voltage trip should not occur, so further investigation is usually required.

Air Cooled Scroll Chiller

 Air Cooled Scroll Chiller


Check the following items before resetting from a low-pressure trip.

1. Make sure your pump is turned in the correct direction. You can check the direction of your pump by carefully sliding a nylon tie through the vent at the end of the pump housing. When your tie comes in contact with the plastic cooling fan, the end will be forced up or down depending on the direction of rotation. If the wire to the end is up, the pump is rotating clockwise, if it is rotating clockwise. At the end of the pump, there is an arrow engraved on the SS head of the pump. This arrow will indicate the design rotation. You pump must rotate in the same direction.   


On three-phase systems only, if your pump is rotating in the wrong direction, stop turning off the main power to the cooler and reverse any two power supplies on the main bus. Turn the power back on and recheck the rotation. On single-phase chillers, if your pump is running in the wrong direction


2. Clean all filters and strainers: restricting the flow through the chiller cooling system will cause Lo 1 to trip. A common problem on PACT and EST systems with integrated water storage tanks is a clogged filter located above the tank recirculation pump discharge. Turn off the power to the chiller and clean the filter before proceeding with any other steps. For all chiller models, the factory recommends installing a strainer or filter on the FROM PROCESS loop line to prevent debris from entering the chiller. If you have an ES, PAC system, such filters and strainers must be cleaned as they can cause low flow errors.


3. Make sure your LP micro trip point is set to 54 PSI.


4. Make sure your SP Micro is set no lower than 45F.


* If your process requirements require a setting lower than the above, you must use glycol freeze protection to prevent Lo 1 from tripping and provide freeze protection.

Air Cooled Screw Chiller

 Air Cooled Screw Chiller   


5. If your chiller is equipped with the full liquid condenser option, make sure that both liquid refrigerant main valves entering and leaving the receiver are fully seated against the back - open. These valves are shipped from the factory in the closed position.


6. Make sure all wires on the back of the microprocessor are securely connected. If there are any excess shield wires on the gray transducer cable shown, tape the area with black electrical tape. Make sure no stray wires from the micro are touching the housing or any other wire connections on the back of the micro.


7. Is the cooling system undercharged? A quick reason to determine low charge is to install a manifold gauge set on the high and low pressure side of the refrigeration system. After resetting the chiller and compressor start-up, look carefully at your gauges. A pitch to design the high pressure side pressure is ambient +30 converted to PSIG. A pitch to design the low pressure side pressure is the chiller, which converts fluid temperature -5F to PSIG. Example: An R-22 system at 60F ambient temperature with a 50F chiller leaving temperature will run about 175 PSI on the high pressure side pressure and about 60 PSI on the low pressure side pressure. If both pressures are low, it is recommended that a leak check be performed.


If 1-7 above does not resolve the low pressure trip problem, it is recommended that you call the factory for further support.


For more information

The recommendations in this article should be performed by qualified service personnel with extensive experience in high voltage/control electrical and plumbing systems. Individuals lacking such experience may damage this equipment and such damage is not covered by warranty.

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