Figure 1. (Click on the image for an enlarged view.)

In this troubleshooting situation, we have a customer who has called to say that their 12,000 Btu through-the-wall unit is “blowing cool air even though it’s set for heat.”

Here’s the unit’s profile:

1.It’s a heat pump with a three-speed motor.

2.It operates on 240 vac.

3.There is no step-down control voltage system for mode selection or temperature control, only the push-button and thermostat control on the unit itself.

4.A dual capacitor is employed and both the compressor and fan motor are PSC-operated.

Upon your arrival, you find the following conditions and get the following results with your electrical tests:

1.The outdoor temperature is 50°F.

2.The indoor temperature is 65° and the unit is set in the heating mode with the thermostat turned up to a maximum setting. The compressor is running and the blower motor is operating on high speed.

3.A voltage check at C on the capacitor (see the Figure 1 diagram) and L1 on the switch shows 240 vac.

4.A voltage check at RV shows 240 vac.

Your troubleshooting question: Which component has failed?

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Publication date:09/06/2010