Troubleshooting Puzzle: A Light Commercial Air Conditioner That’s Blowing Warm Air
In this troubleshooting situation, the customer’s complaint is that their office air conditioner is “not cooling at all.” When you arrive, you confirm that the indoor air temperature is far above the standard comfort level, that the indoor fan motor is operating, and that the thermostat is properly set to call for cooling.
The first thing you note when checking this rooftop unit is that the lockout relay system has done its job of shutting down the compressor operation (note the schematic in Figure One), and you also note that neither outdoor fan motor is operating.
Click to enlarge
Figure One: (Courtesy of Jim Johnson)
When you check the schematic, you also confirm that the lockout system is not designed to shut down the outdoor fan motors in the event of an overload situation, and when you disconnect the power supply to reset the lockout, then reconnect the power supply, you find that the compressor starts, but the outdoor fan motors do not operate.
As your next step, you turn the off the power supply, disconnect one wire from the 240-volt contactor coil, and turn the power supply back on. As your next step, you accomplish a voltage check at the OFC coil, and your reading 240-Volts. Next, you perform voltage checks at the outdoor fan contactor contacts wired in series with the outdoor fan motors and find that in each case, you read 240-Volts.
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