Most of us have seen this problem at least once: a heater/AC blower switch that only works in the high-speed position. It’s not a serious issue for some of us, and in fact many might not bother to fix it at all. Mostly, it’s a pain in the neck. When it drowns out the radio, you turn up the volume, and when your passenger wants to talk, you turn the fan off. That is, unless (heaven forbid) you swerve off the road while toggle the AC switch on a hot summer’s day.

Fortunately for the owners of 2004-2008 Ford F-150 trucks, the most common source of the problem isn’t the fan itself, but the heater switch resistor located right behind the switch. Dusty Bumpers of Ford Truck Zone ran into this problem, and he was thoughtful enough to share the repair with the rest of us, along with some great photos. Thank you Dusty Bumpers!

The resistor has a large flat end that connects it to the switch, and a wiring receptacle at the other end (the left side in this photo). It is held in place by a pair of screws accessible from behind the dash.

To access the resistor, the glove box must be fully open. With the glove box in its normally open position, carefully depress the right side of the box inward, toward the driver’s side of the cab. When the stop tab is able to clear the glove box opening, pull the box fully open, allowing it to hang by the bottom hinge.


Heater fan resistor, as seen from behind the dash


Remove the 2 retaining screws.


Depress the tab on the harness connector and disconnect the harness. Remove the resistor by pulling it straight out.

Install the new resistor in the reverse order of removal.

IMAGES: All images and descriptions are the property of DustyBumpers licensed to FordTruckZone and may not be used without consent.