So my car started overheating the other day in standstill traffic, while driving it's perfectly fine. Got home and discovered my radiator cooling fan isnt coming on. Checked my fuses and relays for the high and low speed all were fine. Fan wont even come on when I turn the ac on. Tested the fan and its fine. What else am I missing? When I turn the ac on I can hear a grinding noise that sounds like its coming from the fan, replaced with a new fan and same thing. My idle rpms also drop significantly when turning the ac on now. Any ideas on what to look at? Could a bad thermostat or cylinder head temp sensor cause the fan to not come on?

 

Wiring diagram of the cooling fan:

http://iihs.net/fsm/?dir=40&viewfile=Cooling%20Fan.pdf

Here's where else you check. Need to go to the Bussed Electrical Center:

http://iihs.net/fsm/?dir=40&viewfile...nformation.pdf

There you'll find the PCM Power Relay (which should be fine) in the 'upper left' of the box (If you turn the PDF file counterclockwise so that it's reading left to right correctly, and then zoom in on it.)

The High Speed Cooling Fan Relay and Low Speed Cooling Fan Relay are the second and third big relays from the left on the bottom row.

Again, it's unlikely in the extreme the PCM relay is out. But it's kind of likely that one of the two relays for the cooling fan might be out, most likely the low speed one.

They should be swappable, and are fairly common type relays, but those are relatively easily tested as well.

If those aren't it, and the fuses at F3 and F40 are ok, and the fan itself is fine, then the only remaining thing is something with the PCM (Engine control) and you need to take it to the dealer/reputable Ford guy/get a scan tool at that point, my opinion, to have the computer tell them/you what it thinks is wrong. It could be any of the things you said or something else.

Fuse F3 is a 40A box fuse, left side, lower two, upper one (confusing, right? ) in the diagram.

Fuse F40 is a 15A blade type, just 'under' the PCM Power relay's right side in the diagram.

Hope that helps! Good luck!

 

Looks like the fan may have shorted and it burnt up a wire in the power distribution box.

 

Wiring harness was repaired and still no luck. My mechanic said the PCM may have been damaged as everything else checks out. Sourced a fairly cheap replacement gonna have it reflashed and hope for the best.