Fan malfunction

Reply Subscribe

Thread Tools

Search this Thread

Jul 14, 2019 | 03:12 PM

Koolerdog

Thread Starter

New User

Joined: Jul 2019

Posts: 2

Likes: 0

Fan malfunction

7.3 super duty deisel
Fan motor only works on high. Replaced fan resistor(male & female due to corrosion), 40a fuse in dist. box is good. What next?

Jul 14, 2019 | 07:35 PM

projectSHO89

Hotshot

Joined: Jan 2004

Posts: 19,768

Likes: 1,082

From: St Louis

Explicitly identify what you are working on.

Jul 14, 2019 | 07:42 PM

Koolerdog

Thread Starter

New User

Joined: Jul 2019

Posts: 2

Likes: 0

'99 F250 super duty

Cab fan switch only works on highest setting. Replaced resistor (both ends due to corrosion). Still won't work except on high. Fuse in power box (40a) is good. What's next?

Jul 15, 2019 | 09:23 AM

SDSC4X4

More Turbo

Joined: Dec 2012

Posts: 565

Likes: 33

From: Newcastle & Gillette WY

The circuit (+) goes from the fuse through the motor to the resistor, then separate conductors from each resistor (-) go to the switch which selects the fan speed based on which resistance path is grounded. The connector at the resistor can overheat and corrode, that is usually obvious visually. There is a connector at the switch, again failure is obvious. It is most likely the switch itself. The back of mine is a white molded panel that discolors if it goes bad, you have to remove it from the dash and inspect the back of it.

You can also use an ohm meter to test the various switch contacts. The resistance should be the same from the ground pin through each of the other pins. The fact that you have high speed indicates the ground is OK.