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2004 Chevrolet Monte Carlo heater fan

Heater Fan stays on with ignition off

There may be a relay that provides full power to the heater fan motor when the speed selector is turned to high. If this relay is defective, it may allow the heater fan motor to run continuously as it bypasses the ignition switch and draws power directly from the battery. If you can locate the relay,pull the connector off. If the heater fan motor stops, you have found the problem. You will still have the lower speeds on the fan motor. You will just lose the highest speed.