Service & Maintenance / Extra Edition

Troubleshooting Challenge: A Heat Pump That Kicks Off

In this month’s troubleshooting problem we have a customer who can only tell us that their heat pump “isn’t working” and “the temperature in the building isn’t right.” When you arrive, you confirm that the system isn’t operating properly. The indoor fan motor is running normally, but the building temperature is far from the thermostat set-point. Satisfied that the problem is not with the indoor section of the equipment, you focus on the outdoor unit, using the partial schematic diagram in Figure 1 to become familiar with the components and circuitry there. (Click here to access a PDF of Figure 1.)

When you evaluate the situation, you find the following:

1. Contacts 11 and 21, and 13 and 23 are closed.

2. The compressor is hot and off on overload.

3. The OFM is very hot and attempting to operate.

Your next step in isolating this problem is to turn off the power supply and disconnect the appropriate wiring in order to check the following, with these results:

1. A digital meter test from C to H on the dual cap shows 55 MFD.

2. A second test from C to F shows 5 MFD momentarily, then the meter display shows a series of higher and lower MFD readings, then all zeros, and then begins reading random numbers again.

Your troubleshooting question: What is the specific failure that is preventing the outdoor fan motor from operating?

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

Publication date: 11/5/2012

PDF - November Troubleshooting Answer

For information on Jim Johnson’s HVACR technician training DVDs, go to

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