Service & Maintenance / Extra Edition

Troubleshooting Challenge: A Split System Heat Pump That’s Not Cooling

November 4, 2013
Our troubleshooting problem involves a split system heat pump in which the outdoor unit is operating in an 85°F ambient, and when you arrive in response to the customer’s no cooling complaint, you find the indoor fan operating normally, and you also note that 240 volts is read at L1 and L2 of the outdoor unit. (Click here for a PDF of the wiring diagram.)

As your next check, you test for the required control voltage at the Y and C thermostat connections because you note that the compressor and outdoor fan motor are both not operating and are cool to the touch. Your meter shows 24 volts at this test point, but 0 volts at the contactor coil. A check at the low-ambient control also shows 0 volts, and a check at the high pressure switch shows 24 volts.

When you manually reset the high pressure switch, the compressor starts, but the outdoor fan motor does not. Your subsequent tests show the following:

1. 0 volts read at the outdoor fan motor leads.

2. 240 volts read at the defrost timer motor.

3. Infinity at 1and 2 on the defrost timer.

4. Infinity at 2 and 3 of the defrost timer.

Your two-part troubleshooting question: What is the next step you need to take in servicing this equipment, and what is the sequence of events responsible for the failure of the equipment to operate properly?

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

Publication date: 11/4/2013

PDF - November Troubleshooting Answers

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

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