Hello all I'm new here and have a issue I think!
I bought my F150 used a couple of months ago. its been many years since I've had a full size truck and I love it.
When I turn it on and turn on the A/C after its been sitting over night the cooling fans will kick on almost immediately, I think they are kind of loud and the Truck isn't hot yet ! Now if I don't use the A/C they don't come on. (is this normal? )
Could this be a bad A/C pressure sensor ? I'm puzzled.

 

Cooling fan has two speeds, low and high, they will automatically turn on when the ac is turned on.
From what you've said it only operates on high speed.
I would first replace the low speed relay and see if that fixes it, its cheep and super easy.
Honestly I don't know how to test the low speed fan without using the ford obd2 program, there is a civilian program called forscan which people seem to like, it may be able to do command the fan on and off so you can test it.

 

Thanks for the input. I will definitely check that low speed relay.

 

OK, so this is what I did. I pulled the Low speed cooling fan relay out, then pulled the High speed relay and put it into the Low speed spot ( they are the same relays). The Low speed fan came on, BUT when I put the Low speed relay that I pulled first and put it into the High speed spot they both kicked on High again. So would that tell me the original Low speed relay is bad ??? what are your thoughts?

Thanks,

 

I think you said you switched the relays and the issue is still present, you could just replace both relays to start and see what happens(doesn't sound like it would fix anything but its only like $15) or if you'd like I can post the wiring diagram, do you know how to read wiring diagrams and complete electrical tested?

 

Yes, only when I put the relay back into the High speed did both kick back into High again. However when I pulled both and put back in again it acted normal, but later the high came back on. After driving awhile the High will cut off. The wiring diagram would help. My son is an electrician so he would be able to help with testing. if all else fails I guess I can take it to a shop or the dealership for a diagnoses. I always try to solve myself. Also I have done a lot of research, could this be an expansion valve issue ?
Thanks

 

Here is the wiring diagram and connector view you may need.
I guess the first thing I would do it unplug the PCM and apply a ground to wiring harness pins 18 & 34, based on the wiring diagram when ground is applied to pin 34 both fans run at low speed since they are wired in series but when ground is applied at both pins 18 & 34 they will run at high speed since they are wired in parallel. Applying a ground like this will simulating the PCM commanding the fans on.
Please note exactly what happens when you do either and how each fan reacts so we can determine the next step.
Why are you asking about the expansion valve, is your AC not working correctly? Like I said originally its normal for the cooling fans to come on when the AC is turned on.

 

No the A/C is working good. I was watching some YouTube videos and it showed if the A/C pressure was too high and it would make the fans run on high, it turned out to be a faulty expansion valve. Thanks for the wiring diagram.

 

Here is a thought, What if I pulled the High speed fan relay out to keep the from coming on High, would that cause any problems ??

 

Here is a thought, What if I pulled the High speed fan relay out to keep the from coming on High, would that cause any problems ??