Service & Maintenance / Extra Edition

Troubleshooting Challenge: A Heat Pump That Won’t Cool

September 5, 2011
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In this troubleshooting situation, the equipment you’re servicing is a 240-volt, single-phase split system in a small office, and the customer’s complaint is that the system is blowing warm air. The customer also told the dispatcher that the office had the same problem at the beginning of the cooling season last year, at which time a different company was called out, and a part was replaced. According to the customer, the unit operated OK until now.

When you arrive, you find the while the indoor and outdoor fan motors are operating, the root of the problem is that the compressor is attempting to start, but kicks off on its overload. When you remove the access panel, you check the schematic and note the wiring configuration for this compressor, shown in Figure 1.

However, when you survey the equipment, expecting to find the two run capacitors (Ca and Cb) wired in parallel (meaning that their value will be added to provide the proper PSC circuit for the operation of the compressor, while only the Ca capacitor will be used in the off cycle to provide a trickle circuit through the start winding), you discover that the wiring has been modified and the compressor circuit now only employs one run capacitor as shown in Figure 2.

Your troubleshooting question: What is the specific cause of this compressor’s failure to start?

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

Publication date: 09/05/2011

PDF - September Troubleshooting Answer

For information on Jim Johnson’s HVACR technician training DVDs, go to www.technicaltrainingassoc.com/HVACRVideoStart.htm.

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