1997 F-150 XLT
Seems to be a common problem for the awesome fuse 5 to blow. I've narrowed it down to an A/C issue so far. From what I've gathered doing my own troubleshooting and from reading, its a short somewhere after the purple wire to the HPCO switch on the accumulator. I've jumpered the HPCO switch and still blows so I'm trying to figure out the problem areas that are between the purple wire at the selector switch to the HPOC.

 

See circuit diagram. The switch on the accumulator is the cycling switch. The HPCO is located on the hard line between the compressor and the condenser.

Use your ohmmeter to check for the short circuit. The clutch coil should be 3-4 ohms.

 

Looked at that in the haynes,
So the purple wire goes to the switch on the hard line first? Same thing there, I should be able to jumper that connection to rule it out?
And will the compressor still read anything with the meter if the clutch is not engaged?
Cant engage the clutch otherwise since it always blows the fuse.

 

Still working on this. Looks like I can unplug the connection on the canister on the firewall and the fuse doesnt blow. Of course, the AC doesnt work since its unplugged....
Any ideas?

 

Also checked the conductivity between all the various connectors and there isn't any breaks.

 

You need to ckeck for shorts to ground.... that's what causes fuses to blow.

 

Ok, so this is what I've come up with.
With the clutch cycling switch on the canister unplugged I can turn the dial to AC and the fuse doesnt blow. Telling me that the "short" is between that switch and the PCM or the switch and the large connection point on the firewall. I undid all the tape and inspected the black/yellow wire and didnt find any breaks. But when I tested for a short I was getting a ground signal.
I was testing with a test light. Power lead to the battery with the pos and neg hooked up to the truck from the battery, then probed the clutch cycling switch black/yellow wire and got a ground signal. That tells me that there is a short, am I wrong?
I've got to be missing something here. ....

 

Get your ohmmeter out and check for the short to ground. Normal reading is about 3-4 ohms for the clutch coil. Any reading of (about) less than an ohm represents the short.

 

OK, so at the plug on top of the compressor I have 3.4 ohms. On the plug that would plug into the compressor I have 1.9 ohms.
Where to check from here?

 

Got it fixed!
Turns out there is a break in the wiring somewhere between the cycling switch and the compressor, blk/ylw wire.
I cut the wire after it splits to the PCM and a few inches after the compressor plug and ran a new hot wire between those and it fired right up.

Now if I could only learn to not procrastinate so much on a 30 minute fix.

 

there is a bundle of wires that run between firewall and motor if the little clip that holds it in place fails it could fall on exhaust manifold (passenger side near firewall ontop of tube thats wrapped in some fuzzy type of insulation) once i fixed the melted wire every thing worked fine (thats what was wrong with my truck)