Compressor Contactor Failure

Issue:

Compressor Contactor Failure

Resolution:

• This diagnostic occurs if compressor proving input(s) on the SCM/MCM (1U49) does not open within three seconds of the call for lead compressor on a circuit to stop or the input is closed when all compressors on a circuit should be off.  
• The unit controls assume that the compressor contactor has welded closed.  
• The input on the SCM/MCM (1U49) 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) unit wiring,
b) switch operation/bad contactor,
c) control module

Here are the steps for Intellipak Air-Cooled Chiller

Step #1 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 #2 Switch/Contactor Checkout

• Disconnect power from the unit.   
• Verify compressor contactor is open.  With an ohmmeter, verify auxiliary contacts are also open. 
• If no problems are found, continue to the next step.

Step #3 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  Compressor  Contactor Failure diagnostic appears, the input/board is good.
• If not, replace the SCM/MCM (1U49).

Facts:

• Intellipak Air-Cooled Chiller 20-60