This client called because their air conditioner would not stop running no matter what he had the thermostat set at. When we shut the thermostat off entirely, the air conditioner would shut off. This tells us that the issue was unrelated to the furnace control board. After some investigating, we found the low voltage wiring outside to be completely dry-rotted and the casing to break off. Without the casing and the wiring left bare (photo above), it created a short between the 24 volts common and the “Y” air conditioning wire. This caused the contactor (photo above) to short out and stick in the closed position. I replaced the low voltage wiring and the contactor. Fired the unit up and fixed the issue.
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