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A Troubleshooting Problem: A Heat Pump That Won’t Cool

Troubleshooting. It’s what we do as an HVACR technician. And, when it comes to troubleshooting, there are some simple steps to understand about the process. Here’s one way to get to what we understand is the bottom line about our job…..figure out what’s wrong, fix it, and get paid.

First, what is the specific type of equipment?

Second, what is the customer’s description of the problem? (Don’t write this one off because the customer isn’t a technician. People are familiar with the sounds, feel, and performance of their HVACR system.)

Third, what kind of history is there regarding repairs on this equipment? Who has worked on it before? What did they do?

Fourth, what is the sequence of operation when this equipment is working properly?

Fifth, what are the symptoms you encounter when you evaluate the operation of the equipment?

Sixth, what specific troubleshooting information is available from the manfacturer regarding this particular piece of equipment?….fault codes?….wiring diagrams?….step by step diagnostic procedures….service bulletins?

And, while you consider the steps above, determine the correct answer to the following problem:

The equipment is a 240-volt, single-phase split system heat pump, and the customer’s complaint is that there is “no cooling.” They also tell the dispatcher that they had the same problem at the beginning of the cooling season last year, at which time a part was replaced and the unit operated OK until now. When you arrive, you find that while the indoor and outdoor fan motors are operating normally, 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 below in Figure One.

Figure One


However, when you survey the equipment, expecting to find the two run capacitors (Ca and Cb) wired in parallel (meaning that their value would be added to provide the proper PSC circuit for the operation of the compressor while only the Ca capacitor would 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 below in Figure Two.

Figure Two


What is the specific cause of this compressor’s failure to start, and what do you need to do in order to get this unit operating again?

Until next week,

Learn from yesterday…..Live for today…..Look forward to tomorrow.