Looks like the schematic shows the diode between the low pressure switch and the A/C clutch, but I can't find the thing. I read a couple posts where folks said it was in one of the fuse/relay panels under the hood, but there are no items with "A/C" in the description and the only item with the word "diode" is the PCM diode, but that's not it...is it?

Thanks in advance for any assistance.


EDIT:

First off, I'm a maroon. I'm working on the wife's truck, which is a 1997 Expedition, mine is a '98 F-150.

Second, I should really have posted some history. Also, I see the diode is in parallel, fails open, and probably isn't the issue...

Couple/few years ago the A/C stopped working and I found part of the clutch sitting on a frame member. So, I put it back and all was fine. Then about two months ago the A/C would work intermittently, when it did come on it would work awesome as usual. Eventually it stopped altogether. The clutch gap was double what it should be, so I pulled out the last shim and the gap was good, maybe a bit on the tight end. Turned on the A/C, still no worky. Checked power at the low pressure switch, good. Jumper the low pressure switch, still no worky. Then I pulled the connector to the clutch coil and there was power at the switch, yay! I figured now it's probably down to a bad coil, but the coil connectors looked a little crummy so I hit them with electrical contact cleaner and put it back. Turned on the A/C and it engaged, but sounded a little crappy and sparks were coming from the front of the clutch assembly when it was engaging, or trying to engage...?? Now, I check power at the coil connector, nada. Still have power at the low pressure switch though. At this point, I could care less about the clutch, or compressor, I just don't want to be chasing burnt wire all over the place. Any ideas?

 

how are you testing the pressure switches - just shorting them and seeing if things kick in? i am trying to debug my AC and not sure how to troubleshoot. I am also 98 F150 - got any pics showing locations of the switches? the low pressure switch is at the charging port? i can check the compressor coil for continuity and power. can i fix clutch shim clearnace without pulling the compressor?

i have a few questions... thanks in advance.

 

Correct, shorting with a paperclip as I've read elsewhere. This was a little weird to me though. I'm used to shorting signal, not power. Perhaps this switch is just a break in a single line, so jumpering it allows continuity? I didn't like it, t'was a little sparky.

First thing to do is look at the front of the compressor, is it spinning? If not, jumper the connector on top of the dryer on the firewall, just above the low pressure fill port. If it engages, either the switch is bad, or the system is low, or the fuse is blown (check your reverse lights). You should probably only jumper it for a few seconds because it's bad for it to run while it's low. If your A/C worked killer and then suddenly quit, I'd replace the switch. If slowly degraded, I'd fill it. Remember that the compressor must be working for it to fill, so you'll need to jumper it again while you fill. If you really need a pic, I can get a pic, but it's above the low pressure fill port, kinda hidden behind that big mess of wires and connector blocks.

You can absolutely shim without pulling! I've done it a couple times now, it's a bit of a pain. Ford makes a special tool to hold the outer portion of the clutch while you loosen/tighten the main fastener, I think it's worth buying/making just to make life easier, plus I love special tools. If you have to, you can replace the whole clutch & coil without pulling the compressor, or discharging the system. Just pull the main bolt in the middle, then use two screwdrivers to slide it off. The pulley part of the clutch slides off pretty easy and the coil seems to be a bit more snug, still totally doable.

 

Cedew - gret help and thanks. i jumped the dryer switch and things started happening - clutch engaged intermittent and roughly and quickly lots of smoke from the compressor clutch so quickly stopped that. i figure i need a new coil/clutch assembly. i notice these are $125 or so - whole compressor is $190 - smart money (at 125k miles) may be to replace the whole compressor? then do i have to do a dryer, freon and some other bits too? we are past fuses now but i'll have a go at it. any suggestions?

 

is this the tool?
http://www.autozone.com/autozone/acc...-Tool/_/N-263f

 

I'd agree that replacing the whole thing is better, but I like the idea of doing it all in a few hours without having to take it in and have it filled, so I would just do the clutch assembly. If it's a well known thing that the compressor is pretty much guaranteed to fail soon after the clutch, then I would do them both, but I haven't read anything that indicates that. I'm no expert, so I have to rely on the interwebz.

That tool looks correct in concept, but it looks like the gender of the three attachment points is backwards. I think you need three holes instead of three pins.