Bryant Fan-Only or Control Board Misoperation

Furnace blower starts and stops repeatedly without burner ignition; cool air may blow briefly.

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.

Possible Causes

Stuck fan relay, miswired thermostat (G energized), faulty limit switch sending false signals, control board logic fault

Safety first: Turn off power before accessing wiring.

Thermostat mode: Confirm thermostat is not set to FAN ON or COOL.
Check thermostat wiring: Ensure only R and W are connected for heat-only operation. Remove G at the furnace to see if the behavior stops.
Inspect limit wiring: Loose or shorted wires on the limit circuit can cause erratic blower operation.

If the blower cycles erratically with correct thermostat wiring, the control board may be defective and require replacement.

Medium 3/5

Furnace Control Board

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