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 with 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. Compress 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.
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.