I have a '95 F-350 XLT pickup with a 7.3 powerstroke. I was driving down the highway, with the A/C on, and all of a sudden, it started blowing hot air. I brought it home, put a manifold gauge set on the system. Shows about 110 on both sides when a/c clutch is off. Pressure is normal when the clutch kicks in, but the clutch has a mind of its own. It comes on when it wants. I can't make it come on, even on Max a/c. When the a/c clutch is engaged, a/c gets cold, so compressor seems to be okay, and refrigerant is intact. Sometimes the a/c works - sometimes it doesn't. Oh, and I shorted the low side switch, and there was no change. What's happening? Thanks...

 

Vacuum issue I bet. One way or the other the control-doors aren't working properly.

*edit*
The compressor is also controled by a temperature switch on the evaparator - that's why you can seem to control it. Once the evaparator hits a certain temperature it shuts the compressor off... So you don't get a big block of ice I believe.

 

I checked all of the vacuum lines and the blend doors, etc. Everything is working
fine. I have air coming out of all the registers, and it will get cold IF & WHEN the a/c clutch comes on. The clutch just doesn't cycle like it used to. Plenty of refrigerant in the system, and the compressor works great when the clutch kicks in. When the compressor is running it doesn't short cycle. But if you turn the a/c off and then back on, the clutch won't kick in for a long time -- if it does at all. This is really a mystery... Any more suggestions?

 

could have a defective high or low pressure switch too

 

Powerstrokedude, your in luck. I just had the same thing happen to my truck. The high pressure switch at the the back of the compressor, the one sticking up off the compressor????? Turn the system on max a/c and walk back to the front of the truck and wiggle that connection. I bet you a dollar it comes on. My a/c clutch was acting like it was slipping, or not coming on at all. Same simptom, driving down the road, all the sudden hot air. Remove that connector and clean it with carb cleaner or something of the sort. But if I remember correctly there is a pin lock you can take off to further clean it once you take it apart. Then I took a sharp pic and put a small dent in the female pin recievers to make a better connection. Works like a charm. I really hope that helps man. Good luck.

 

I too have just suffered this malady on my 95. The problem was with the size of the gap between the compressor and the clutch. The gap should only be about the thickness of a piece of paper. The gap gets wider as the components wear and eventually gets so wide that the magnet can't pull the clutch in, especially if the voltage happens to be a little low at that particular time due to lots of stuff running at the same time. This accounts for the "mind of it's own" characteristic that you describe. The fix is easy. There is one bolt holding the clutch on the front of the compressor. Take it out and remove the clutch. Look up inside the hole in the clutch and you should find a shim (looks like a little washer). Take it out and reassemble. Takes about 5 mins. By the way, my brother had the same problem with his 99 PSD and it cured his too....

 

FYI: The gap should be .014 to .030.

 

Ok, Guys... I finally got some time to look at the problem, and this is where I am now: Concerning the connection at the back of the a/c/ compressor -- I did everything to that connection that can be done, and still nothing. I also removed the 5/16" bolt that holds the a/c clutch assembly, and I couldn't find a shim anywhere. While the truck was running, and all of the a/c controls on high, I attemped to "help" the clutch with a screwdriver, by pushing it toward the compressor. Still nothing. Refrigerant pressure is still good. A/C will get really cold when the compressor clutch kicks in, but that doesn't happen very often. One thing I haven't tried: checking the voltage at the compressor clutch connection. I'll have to go buy a volt meter, but heck, I'm always needing one anyway. Any other ideas? Thanks!

 

Here's another check for you. With the truck off, have someone sitting inside w/ the key on. Have them cycle the a/c on and off. The clutch should engage and disengage. "click, click" If it doesn't and all your connections are clean it's gotta be the clutch coil. I thought that's what mine was, so I looked it up. Oreilleys has the motorcraft clutch coils for like $21. If that connector at the front of the compressor (the two wire connector) is getting a good 12v, I bet you a dollar it's the coil. Easy fix. Hope that helps.

 

I agree with The Duck. When I worked on the big rigs We would see this all the time. Clutch works fine when cool, but as it get hot it loses it's pulling power. my quick check would be to run the a/c for a bit & pull the power wire from the clutch. plug it back after a couple of seconds. if it was bad it wouldn't come back on.