A/C Fan Speed Changing Constantly on Ford F-350 Super Duty

The 2008-2010 Ford F-350 with automatic climate control may have a problem with frequent fan speed changes when using the heater or air conditioner. Normally, the fan speed changes only to maintain a selected temperature, but when the fan speed changes frequently and needlessly, there is an issue with the fan speed control unit.

The fan speed control unit, sometimes erroneously called the blower motor resister, regulates the speed for the blower motor in order to maintain the temperature set by the driver. When it fails, the fan will run at random settings, and the climate control will be inaccurate.

Note: this does not affect the temperature of the air that comes from the vents, it affects the amount of air that comes from the vents.

The repair is simple, and quick. The control unit is located behind the glove box in most models, and removal and installation takes only minutes.

Also note: this only applies to vehicles with single or dual automatic climate control.