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Q: Heater

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heater fan only works on high speed

My car has 74000 miles.
My car has an automatic transmission.

Hi There, This is a sign of a faulty blower motor resistor. Blower motor resistors are resistors which are used to control the fan speed of automotive blowers. The fan speed can be changed either by switching the blower resistor resistance mechanically, using a rotating lever, or electronically by the air conditioning system. The change in resistance then limits the current through the motor, which dictates the speed at which the blower fan works. Blower resistors, being a mechanical component, are prone to wear and are the most common point of failure in a car’s heating system. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

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