HVAC Residential Market / Service & Maintenance / Extra Edition / Air-Source Heat Pumps

Troubleshooting Challenge: A Heat Pump That's Not Operating

Figure 1. Legend: CC - Contactor; CHP - Control, High Pressure; COMP - Compressor; CR - Capacitor, Run; CS - Capacitor, Start; HC - Heater, Crankcase; LACO - Low Ambient Cut-Out; MOF - Motor, Outdoor fan; RC - Relay, Changeover; RD - Relay, Defrost; RS - Relay, Start; TD - Timer, Defrost; THC - Thermostat, Heat/Cool; VR - Valve, Reversing. (Click on the image for an enlarged view.)

 

This troubleshooting situation is actually a look ahead to the upcoming cooling season. Our customer has called to say that their heat pump “isn’t cooling at all,” and while the outdoor temperature is only in the mid 80’s, it’s quite uncomfortable in the house. When you arrive, you find that the underlying reason the unit isn’t cooling is because the compressor and the outdoor fan motor aren’t operating. Checking further, as you use Figure 1 as a reference to troubleshoot this situation, you find:

1. The indoor fan motor is operating and blowing warm air, and the indoor air temperature is just over 80°F.

2. The thermostat is set in the cooling mode with the fan setting at ON. When you change the fan setting to AUTO, the indoor fan motor stops.

3. You get a reading of 24 volts at the LACO terminals.

Your troubleshooting question: What is the next step you need to take to get this unit operating again?

Compare your answer with ours by clicking on the PDF link below.

For information on Jim Johnson’s technician training DVD’s on heat pump electrical system troubleshooting, click here.

Publication date: 01/10/2011
 

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