This diagnostic is created when the unit calls for a compressor contractor to energize, and the contactor does not pull in or drops out during operation. This would normally indicate that a safety (HPC or DTL) has opened, but anything that causes the aux contacts on the contactor to show as open when they should be closed will generate this diagnostic.
If the contactor does not pull in when requested, check wire connections. Poor wire connections in the wire harness seem to be the biggest issue we are seeing, primarily the two pin harness connectors for the HPC's, DTL's, and the compressor contactor coils. (See attached schematic). These connectors are only there for ease of assembly purposes. We have suggested removing them and using wire nuts or splices to correct the issue as a field fix. In many cases, this solves the problem.
Other, less obvious, causes can be a tripped transformer or poor harness connection on the Adapter Board. Compressor Contactors 1 and 2 get their 24 VAC power from the transformer connected to J25 on the Adapter Board. Compressor Contactor 3 gets its 24 VAC power from the transformer connected to J8 on the Adapter Board. Verify that these two connectors on the Adapter Board are receiving 24 VAC. If either of these transformers have tripped, failed, or have a poor harness connection the unit will generate this diagnostic when it calls for the compressor to start.
It is also possible to have a bad aux switch on the compressor contact. If the contactor pulls in, but drops out a few seconds later, check the proving switch and wiring.
A test that can be performed is:
1.) Power down the unit/verify that there is no voltage present on the compressor contactors
2.) Remove the fuses for the compressor or Load wiring to the contactor of the compressor you're troubleshooting (in this example we'll cover CC1/Compressor 1 proving).
3.) Insert a jumper into the P8 plug between pins 4 & 5 (Orange and Yellow wires...see snip below from the schematic).
4.) Power on the unit and verify that the CC1 contactor pulls in and you have 24Vac present on P8 pin 3 (blue wire) for the proving input...if the CC1 does not pull in then there could be a lack of 24Vac, loose connection, or an open safety as mentioned above. If the CC1 does pull in and you do have 24Vac on pin 3 of P8 and you continue to get Compressor 1 Proving diagnostics then there could be an issue with the Symbio 700. You can repeat/copy these steps for CC2 and CC3 (Compressor 2 is the P9 and Compressor 3 is the P10). If everything is working properly the Symbio should trigger a "Compressor X Contactor Failure" diagnostic.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.