Compressor Trip (Compressor Contactor Fail)

https://hub.tranetechnologies.com/docs/DOC-75607

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 auxillary switch on the side of the lead compressor contactor on each circuit. This is a manual reset diagnostic.

Items to check include:

1. safety devices
2. unit wiring
3. switch operation/bad contactor
4. control module

Here are the steps for Intellipak Rooftop

Step #1 Safety Devices

If any of the safety devices, such as high pressure cutout, 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 auxillary 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 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 closes 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 Fail diagnostic appears, the input/board is good. If not, replace the SCM/MCM (1U49).

I have Attached several MCM/SCM Wiring schematic to reference , The one you are troubleshooting should be located on the door panel or you can download one from E-library .

*DIAGNOSTIC
DISPLAYED: Compressor Trip
(Ckt-1 or Ckt-2)
Used With: See
compressor protection     
devices on MCM control
wiring schematic.
Module: MCM

*REASON FOR
DIAGNOSTIC :Problem: There have been
4 occurrences*, during
active compressor
operation, of the
compressor proving input
for the given circuit being
detected open continuously
for more than 3 seconds.
Check: All compressor
protection devices in the
associated refrigerant
circuit's 115v contactor
control wiring circuit.

*UCM’S REACTION: Prior to the (PMR), each
occurrence of a compressor
trip will inhibit all
compressor operation of
the circuit for a period of 15
minutes. After this period
the circuit will be allowed to
restart.
During the (PMR), all
compressors on the
associated circuit will be
locked out and prevented
from operation

* RESET REQUIRED: (PMR) A manual reset1 is
required after this
diagnostic occurs. The
Diagnostic can be reset by
the unit mounted Human
Interface Module or Tracer,
or by cycling power to the
RTM.
Note: *Prior to the (PMR),
if any compressor on the
circuit has 3 continuous
minutes of operation, the
occurrences counter resets
to zero and no error is
generated