Carrier Heat Pump
Diagnose: 2 Carrier Heat Pumps not running. Found no 24V at contactors on both units. Replaced both boards and contactors. 1 unit is now running and contactor pulls in correctly. 2 unit still doesn't have 24 volts at contactor. Switched boards to eliminate a new "bad" board. 1st unit started again with the board that was in the 2nd heat pump and is running correctly. I have 24V on my wire to the heat pump C, R and Y. C=Common, R=Power, Y=Compressor Contactor. I pulled the connector from the board and I'm still reading 24V on the above. So, I've eliminated the board and the connector. I do not have 24V coming out of the board to the contactor.
What am I missing?? Low or High Pressure Switches not allowing the contactor to pull in?? Some help would greatly be appreciated!!!