Compressor Trip CGAF

Issue:

Compressor Trip

Resolution:

This diagnostic occurs if compressor proving input(s) on the SCM/MCM (1U49) does not close within three seconds of the call for a compressor to start or the input opens during compressor operation. The input is connected to the normally open contacts of an auxiliary switch on the side of the lead compressor contactor on each circuit. This is a manual reset diagnostic.

Items to check include:

a) safety devices
b) unit wiring
c) switch operation/bad contactor
d) control module

Here are the steps for Intellipak Air-Cooled Chiller

Step #1 Safety Devices

If any of the safety devices, such as high pressure cutout (see note below), winding temperature limit, or compressor circuit breakers, are open, the contactor cannot be energized and the diagnostic will occur. Verify all safety devices are closed, the 115-volt control fuses are good, and 115 VAC is present. If all the safeties check good, continue to next step.

Step #2 Wiring Error

Verify the wiring between the compressor auxiliary switch and the SCM (1U49 on 20-30 ton units) or the MCM (1U49 on 40-60 ton units). Also verify the wiring of the compressor contactor coil circuit. Refer to unit schematics for wire numbers and connections. If the wiring checks good, continue to the next step.

Step #3 Switch/Contactor Checkout

Reset the unit diagnostic. Using the Service Mode Menu at the Human Interface, turn on the compressor circuit causing the lockout.

If the contactor energizes, verify that the aux. switch closes. Replace switch if it fails to close when contactor pulls in.

If the contactor does not energize, check for 115 VAC across coil. If 115 VAC is present, replace contactor. If 115 VAC is not present at contactor coil, verify voltage is present at the SCM/MCM (1U49). Refer to unit schematics for wire numbers and connections. If voltage is present, the SCM/MCM may have a defective onboard relay and must be replaced. If the voltage is not present at the SCM.MCM, recheck the wiring and safety devices. If no problems are found, continue to the next step.

Step #4 Control Module

If no problems are found in the above steps, the proving input on the SCM/MCM (1U49) may not be functioning. Reset the unit diagnostic and place a jumper on that input. If a Compressor Contactor Failure diagnostic appears, the input/board is good. If not, replace the SCM/MCM (1U49).

 A head pressure control switch may be added on each circuit to the second fan output on the 1U49 MCM Scroll Compressor Module.  This switch closes at 277 psig and opens at 155 psig.  It should be wired across the "B" fan outputs on each circuit while monitoring the discharge pressure off of the compressor. This would help solve a problem if the head pressure rises very quickly when the second compressor on the respective circuit comes on.

Notes:

The Trane part number for the head pressure control switch is CNT02923. 

This does not apply to CGAC chillers, only CGAF.

Verified HPC switch is opening on High Pressure.  Further verification revealed the chiller was selected for Low Leaving Solution (Model Number digit 11).  If the chiller is selected for Low Leaving Solution a 360 psi HPC is installed.  If the Chiller is running water higher than 40 F, then the HPC should be 405 psi.

Changes:

Other Question/Problem/Cause Statements:

• Compressor Trip...Circuit 1 & Circuit 2?
• High pressure switch is opening
• Compressor Trip

Facts:

• Intellipak Air-Cooled Chiller 20-60
• Air-Cooled Chiller - Intellipak (CGAC, CGAF)