Troubleshooting Challenge: A Split System That’s Not Cooling
FIGURE 1: System start components.
In this troubleshooting situation, the equipment is a split system that’s approximately five years old, consisting of a gas furnace to provide heat in the winter, and a condensing unit and “A” coil to provide summer cooling. There are actually three questions to answer in this problem … two of them regarding overall troubleshooting procedure, and the third one regarding the necessary repair.
The information you get from the dispatcher is that the customer’s description of the complaint is “blowing warm air.” Which brings us to the first question about this problem: What are two components located in the furnace assembly that can be eliminated from consideration as the possible source of the problem?
When you arrive, you confirm that the system is blowing warm air. You also confirm that the thermostat is set to the cooling mode with the setpoint below room temperature, and the fan switch is set to the AUTO position. A check on the condensing unit reveals that the condenser fan motor is operating normally, but the compressor is not running. Your second question: What two components inside the condensing unit can be eliminated from consideration as the source of the problem?
After turning off the disconnect switch and removing the access cover, you find that the compressor is hot to the touch, indicating it is attempting to start. Based on that observation, you disconnect all the appropriate wiring when necessary, and, with a digital meter, check the start components shown in Figure 1. You get the following results:
1. At terminals SC, you read the microfarad rating shown on the capacitor case.
2. At terminals RC, you read the microfarad rating shown on the capacitor case.
3. At the SR terminals of the potential relay coil, infinity.
4. At the SR terminals of the potential relay switch, a fraction of an ohm.
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Your final troubleshooting question: What do you have to do to get this unit operating again?
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Publication date: 3/7/2016
For information on Jim Johnson’s HVACR technician training DVDs, go to http://techtrainassoc.com/training-videos/hvacr-training-videos/.
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