All right I'll try to make this post as short as possible but it'll probably be long. I have this AC problem on my truck I went in because the AC clutch went out and they suggest a replace the compressor and the clutch and the evaporator dryer thing. So everything worked fine when it came out of the shop except I immediately noticed the problem that when it got hot outside the AC clutch stopped engaging. In the morning hours it works fine blue cold no problems. As soon as the outside temp got to about 80 degrees the clutch with the stop engaging therefore no cold air. I went in had it checked out they said the refrigerant level is fine and we can't figure out why it's not turning on the clutch. I went back and forth with them forever and they could not find the problem I bring it in in the morning it worked fine it says it's working fine and if I bring it in the afternoon and it didn't work they couldn't figure out why it wasn't working.

So, I discovered that by testing the voltage of the positive going to the AC clutch that it wasn't getting any power at the times when the AC wasn't working. Kind of obvious. So I figured I cut the wire going to the AC clutch and run it to a 3-way switch to where if it's switched in one position then it goes from the computer feed power to the AC clutch like it is stock. If you switch the switch to the other position it goes off straight 12 v switch by the ignition to the AC clutch directly. Now my theory is that because the circuit is separated from the computer completely when it's switched to the brute force method of straight 12 v then whatever is causing the AC clutch not to start through the computer would be bypassed. And therefore if the AC clutch was powered on the AC compressor would turn no matter what. Now one thing I noticed is that by putting a voltmeter on the computer power feed side to the AC clutch it's only putting out .71 v oh, so not even One v. And the AC compressor comes on fine with that. Now oh, is this normal voltage going to the AC compressor clutch? And will it hurt the AC compressor clutch if I manually put 12 volts to it? And when I had it in the shop one time the guy said he put 12 volts to the clutch directly and then clicked on and off. So he said it should be a 12 volt clutch I don't know why it's working with .71 of a v. So anyway this is been a long drawn-out process and I'm trying to figure out and if I have the circuits totally separate to where I I don't backfeed 12 v into the computer is that safe to do and will it work? And any other things I could look at that are causing this problem in the first place when the outside temperature gets warm the AC clutch won't engage I'd appreciate any input. Thanks a lot

 

Do you have a pressure gauge set, where you can read the system pressures when the compressor is cycling ? Sounds like it may just be a little low on freon.

 

Last time I was in the shop for the problem they checked the level of freon and it was perfectly full. Besides, low Freon wouldn't explain why it works fine in the morning and then quits in the afternoon and then it's fine the next morning again. It also wouldn't explain why the clutch isn't engaging when it's not working but it engages when it is working.