The truck is a 93 F150. The problem is that the fan only works on hi. The other 3 speeds do not work. There are 4 wires entering the switch. 3 have power coming in, the 4(black) is ground I assume. The contacts on the switch appear to be fine. Is there any thing else that could be wrong.

 

Somewhere on the heater blower box is a (probably) brown circuit board about 2" to 3" square with a connector plugged into it. On the back of the board are several resistors that control the fan speed. One or more of them is broke or burned open. The part is pretty cheap and easy to change.

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97 Lariet-sc-4.6-4x off road-auto-3.55 LS-
superchip-Airraid-Perma-cool electric fan & controller

 

ford-tough1
when you take the little board out, the resistors are wire wound & surface mounted on the inside. I've tried to fix them but they are ni-chrome with crimped connections. easier to get a new one.

 

Thanks I will check that out.

Is it possible to access the resitors and check the resistance or continuity with a multimeter?