AboutJ Cook Expertise With 25+ years experience, I am familiar with residential, commercial, and industrial HVAC equipment including but not limited to boilers, chillers, reciprocating and screw compressors. I am trained in all manners of control wiring.
Experience I currently have three HVAC licenses and Refrigeration license by the State of North Carolina. I have been in this field for over twenty years. I have been a service technician for a contractor and also worked at a state college in the repair and maintenance of steam lines and equipment. I am currently the Building Maintenance Superintendent for a municipality.
Question I have a Heatpump with the air handler inside. The problem is when I put the thermostat in cool, the blower comes on but not the heatpump. I checked the unit and there is line voltage out there 240V, but I am not getting any low voltage to the contactor. Without running through all the wires I checked the yellow and red and orange. I have not worked on heatpumps very much. My experience is with split unit systems with just a condenser. So that wiring from the thermostat and furnace I know well. Can you please tell me how to check the wires and which ones, also what do you think could be the problem. I also checked for voltage off of the wires on the transformer, but not sure I did it right. There is a brown and red coming off the low V side and they go into a circuit board and then yellow goes to overflow switch in A-coil and red goes into thermostat wire harness. I also can tell you that it is a heatpump with heat selector on thermostat with an auxiliary for heat and then a cool switch. Any diagnosis tips would really help for now and future.
Thanks a lot,
Answer In a heat pump, the Y circuit brings on the compressor whether in heating or cooling. The only difference and it depends on the manufacturer, when the Y circuit makes, it also makes the O circuit usually an orange wire and this controls the reversing valve. This valve again depending on the manufacturer is either powered in cooling or heat mode. Since you have an overflow switch, the Y should be going from the thermostat to the overflow and then to the compressor contactor. Jump the overflow switch and see if this completes the circuit to the contactor. Sometimes these get corroded points and will not make the circuit. The circuit in normal position is made and when water rises, the contacts are broken shutting off the compressor to prevent overflow of the pan. If this still does not bring on the compressor, remove the front portion of the thermostat and leaving the sub base intact, jumper R to Y and see if the compressor starts, if so it may be a defective thermostat. Thanks J
