Service & Maintenance / Extra Edition

Troubleshooting Challenge: A System That’s Blowing Warm Air in July

This month’s troubleshooting situation involves an air-to-air package unit heat pump that is approximately six years old, and the customer’s complaint is that, rather than providing cooling, it’s just blowing warm air.

When you arrive, you confirm that the thermostat is set in the cooling mode and the fan switch is set in the AUTO position, and that no cooling is taking place. Since the single return is nearby in the ceiling, you also check the filter, which the customer replaced before they called for service. The customer also confirms that they replace the filter every month.

When you evaluate the operation of the system, you find that the compressor, outdoor fan motor, and indoor fan motor are all running, so you decide to begin your troubleshooting with the control segment of the equipment. (See the schematic diagram here.) Working at the control voltage terminal board (TB) you find the following:

• 24 volts from the common side of the transformer to “R”

• 24 volts from the common side of the transformer to “G”

• 24 volts from the common side of the transformer to “Y”

• 0 volts from the common side of the transformer to “O”

Your two-part troubleshooting question: What are the two possibilities responsible for the results, and why is the system not cooling?

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

Publication date: 7/7/2014

PDF - July Troubleshooting Answer

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

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