Newbie here so let me know if I'm doing anything incorrectly. Replaced AC compressor, Accumulator, orifice tube and the high side hose assy with muffler on my son's best friend's truck (1999 F-150, 4x4, 5.4L eng) this week-end. His prior compressor was making a horrible noise and was needing to be recharged every 3 months or so until the last time we charged it last summer when it only lasted 3 weeks. I think he had some other problem than losing freon because his charges were lasting several months previously but I didn't troubleshoot it then so I have no way of knowing for sure. Anyway, I evacuated the system and charged it but after the 2nd 12 oz can of freon was going in compressor still wasn't engaging. Checked the plug at compressor and it came loose so I plugged it back up and the compressor clutch started trying to engage several times but only stayed engaged from less than a second to maybe 3-4 seconds tops. It would make several attempts then stop like it was timing out (maybe the PCM smarts possibly). I put 12V directly to compressor and it engaged continuously, the pressures were roughly 45 low side and 170 on the high side which to me seemed pretty close to normal for only 22-24 oz freon (capacity is roughly 34 oz) and outside temps in upper 90s. I tried jumping the low pressure sw on the accumulator and the high pressure sw near the high pressure connector but clutch still would not engage. Also jumped the AC relay power contacts that sends 12 V to compressor and that engaged the compressor (tried it with switch and ac on but truck not cranked and heard the clutch engage). Also swapped the relay with one of the other like relays that were working and compressor would not engage. I've looked high and low on the internet for a schematic but can't find one so I ordered a service manual on CD from ebay but I won't get it until later this week. I could still have a wiring issue from AC dash switch to relay or in the LPS/HPS to PCM wiring and also think it could be the PCM but how many of you folks have had problems with the PCM for AC not working? Any ideas on what else I could check? I did find one AC troubleshooting section that said I should be getting 12V in and out of the LPS and HPS (previously wasn't sure if they were normally open or closed) so I will check that tomorrow night but I don't think those are my problems as jumping them didn't fix my problem. Originally thought it might be an issue with the new (not rebuilt) compressor or clutch but since it worked when I put 12V on it and the pressures "looked" normal, I pretty much took that to mean the compressor and the mechanical stuff is working properly and that my problem is purely electrical. Just FYI, the pressures equalize at about 110-120 PSI but it was really hot here this week-end so I thought that was normal too. Sorry for such a long description but more info is better in my book. Any ideas would be appreciated!

 

Left one thing out. I checked the AC diode with a multi-meter with a diode checker setting and I got nothing, same reading you get when your checking resistance and there's no continuity. I checked it both ways. Never checked a diode before but could that be the problem with the solenoid not staying engaged?

 

No, it's not the diode. It's there for a different reason.

Here's the schematic. See pages 2 & 3. https://dl.dropbox.com/u/75400642/19...0Schematic.pdf

Check CJB fuse F5 first.

 

Thanks project, the schematic will be very helpful. I didn't check the fuse but the compressor was trying to start so it seemed to be getting power at least intermittently. I'll look at it anyway tonight. I have read about the diode since and realize that's for feedback off the electromagnetic clutch and agree that wouldn't be the problem. Have you ever heard of the PCM causing problems with compressor running? I plan to check the fuse and the wiring on the pressure switches tonight to make sure 12V is getting thru there for the PCM to energize the relay. Anything else jump out at you that should be checked before I have to go into the dash?

 

Why is this not in the HVAC section? You'd get more help there.

 

I'm new here and this was the section I found that looked like a good place to post. I didn't see the HVAC section but will re-post there now. Thanks!

 

Do not re-post. It just dorks up the forum.

Ask a moderator to move the thread.

 

That sounds so funny (to me) just the way you worded it projectSHO89 ... but it IS true. If I were a newbie, I probably woulda done the exact same thing. Probably DID at some point!

No harm captaink.... if you don't find your answer here as you hoped, you can PM Bluejay,Rockpick,Patman or several others that have "moderator" or "Administrator" under their screen name.


Welcome to the Site

 

Thanks Red02FX4! Appreciate the info.