Carrier
Continuous Fan Operation
Furnace blower runs continuously even when there is no call for heat or fan from the thermostat.
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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
Thermostat fan set to ON, stuck blower relay on Carrier control board, open limit switch forcing fan on, miswired G terminal
How to Fix / Troubleshooting
Safety first: Turn off power before accessing the control board.
- Check thermostat fan mode: Ensure the thermostat fan setting is AUTO, not ON. If set to ON, the blower will run continuously by design.
- Observe control board LED: If a limit fault code (e.g., 33) is present, the board may be running the fan to cool the furnace. Address the limit issue first.
- Inspect G wiring: With power off, remove the blower door and check that only the thermostat green wire is on the G terminal. Remove any jumper between R and G.
- Test for stuck relay: If the blower runs immediately when power is restored, with no thermostat connected, the blower relay on the control board is likely stuck and the board will need replacement.
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Repair Difficulty
Medium
3/5
Required Part
Furnace Control Board
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