Armstrong Air
Stuck Contactor or Control Signal
Outdoor unit runs continuously and does not shut off even when thermostat is satisfied
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Contactor welded closed, Thermostat stuck calling for cooling, Short between R and Y in control wiring, Faulty indoor control board output
How to Fix / Troubleshooting
Safety first: Turn off the outdoor disconnect immediately to stop the unit. High voltage is present at the contactor.
Steps:
- 1. Verify thermostat: Set thermostat to OFF. If the outdoor unit continues to run, the problem is not the thermostat setting.
- 2. Inspect contactor: With power off, remove the control panel and visually inspect the contactor. If the contacts are welded closed, the plunger will not move freely.
- 3. Test coil signal: With power on and thermostat OFF, a qualified person can check for 24V at the contactor coil. If 24V is present, there is an unintended call for cooling from the thermostat or board.
- 4. Replace contactor if welded: Install a new contactor of the same rating.
- 5. If coil is energized with thermostat off: Inspect thermostat wiring for shorts between R and Y, and have the indoor board checked by a technician.
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Repair Difficulty
Medium
3/5
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