Fraser-Johnston
Runaway Cooling / Stuck Contactor or Control Fault
Outdoor unit runs continuously and will not shut off
Advertisements
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.
Advertisements
Possible Causes
Stuck closed contactor, Shorted thermostat wiring calling for constant cooling, Faulty control board output, Thermostat set too low or malfunctioning
How to Fix / Troubleshooting
Safety: Turn off power at the outdoor disconnect immediately to prevent damage.
- Inspect contactor: With power off, check if the contactor contacts are welded closed. Replace if they do not open freely.
- Check thermostat: Raise the thermostat setpoint above room temperature. If the outdoor unit still runs when power is restored, suspect wiring or control issues.
- Inspect low-voltage wiring: Look for shorts between Y and R in the thermostat cable or at the air handler board.
- Control board: If the board is sending 24 VAC to the contactor when there is no call for cooling, replace the board.
Advertisements
Repair Difficulty
Medium
3/5
Advertisements