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So on my 2002 f-350 7.3 I noticed towards end of last summer my a/c would cut in and out at times, ignored it all winter obviously and now its getting hot again I'm paying for my laziness with an A/C system that doesn't work at all. Found my compressor clutch isn't engaging when the a/c control is turned on, checked for power by back probing connector at compressor and no 12V. Checked refrigerant with gauges all looks ok, checked for power at both high and low pressure switch by back probing and both have 12V. Checked fuses obviously but don't think is a power supply issue bc I'm getting power at those switches. I've seen on some wiring diagrams it looks like only other items in that circuit is the PCM and a diode? I don't think my set up has a A/C relay or at least I haven't been able to find anything below dash or under the hood, not sure where I could be losing 12V from. Any insight is much appreciated!
Try jumping the pressure switch on the accumulator. If the clutch kicks in and everything else checks out like you say then the switch is bad and a new one should fix it.
If jumping the switch doesn't trigger the clutch coil the the coil is likely bad. Jump it straight to battery, if still no love it's definitely bad. If it kicks in then you've got a bad wire or connector. Hold on, check the resistance across the high pressure switch. I can't remember if it's a make or break switch, but either way, if it's reading open you can jump it. If closed unplugging it should bypass it. If it's bad and tripped for high pressure it prevents the clutch from engaging.
Its not the air gap bc its not spinning the clutch at all. I should have mentioned I tried jumping clutch to battery and its engages no problem and a/c blows cold. I also tried unplugging both and bypassing both but now that I think about it I may have had both unplugged while trying to jump it so let me give that another go and report back.
If you have power at the switches, and the clutch engages when you jumper it, it's a wiring or switch issue.
Measure resistance across both switches, when the compressor is static they should both be closed (0 ohms) if there is enough refrigerant in the system.
Another very common failure is the plug on the compressor itself... the wires fatigue where it bends coming out of the plug and fail.
Try wiggling the wires going into that plug when the system is commanding the compressor on.
Another very common failure is the plug on the compressor itself... the wires fatigue where it bends coming out of the plug and fail.
Try wiggling the wires going into that plug when the system is commanding the compressor on.
Over the past, I've had that connector cause problems with compressor starting at least (3) times. Happened with my 1995 Dually.... and twice with my F250. Learned to make sure I'm not laying on that connector if working on top on engine for sure!
Sry for delayed response but I went ahead and jumped out both switches and still no engagement of the compressor. I checked 12V at both switches which I have and I bought a replacement connector for the compressor plug and jumped that straight to battery and compressor engages. Wired that plug to the original harness for the compressor plugged it back in and still nothing have no 12V at the plug side of the compressor harness. After looking at multiple wiring diagrams its appears only other items along that circuit is the ECM and a diode, if anyone knows where the diode is placed that would be a huge help? Or if anyone has and idea for bypassing the ECM output? Thanks!
The AC diode is in the relay/fuse box in the engine bay. There are 2 diodes here. The one for the AC is bottom (front of engine) passenger side - #36 in the manual, pictured below. The other diode is for the PCM.
Are you getting power to the first pigtail that comes off the cowl prior to the first switch in the circuit? If so, you're issue is down stream. If not, chase it proximally. For me, it was the low pressure sensor but if you jumped it with a paper clip/wire in the correct 2 pins, I'm sure we can omit this being the culprit. I bring it up though due to when my sensor was bad, the diode also was not getting power. The issue was not the diode, but in the circuit itself. If it is a wiring issue, the harness is pretty easy to trace continuity with a multimeter in the bay. If no continuity, it's also easy to pull out the entire harness out (2 sensor pigtails, pigtail at the cowl, ac clutch pigtail, and a plastic bracket on the dipstick). Fish it out and pull the wire loom back to inspect the wire insulation where continuity is being lost to see if you had a varmint get the late night munchies.
There are multiple factory wire splices in this mini harness for the AC system and any one of them has the potential to fail. Heck try a voltage drop test. Maybe you've got a weak connection that's only showing itself under a load.
I've seen that fuse box diagram now a few times but for the life of me I can't locate any other fuse box except the one under the steering column. I'm getting power to that first pigtail but it comes out of that small harness on the passenger side as a black and pink wire I believe but its a gray wire on the plug for compressor that should have 12V. Good ideas on the continuity test and voltage drop test on the harness and circuits I'll go over that and report back.
I've seen that fuse box diagram now a few times but for the life of me I can't locate any other fuse box except the one under the steering column. I'm getting power to that first pigtail but it comes out of that small harness on the passenger side as a black and pink wire I believe but its a gray wire on the plug for compressor that should have 12V. Good ideas on the continuity test and voltage drop test on the harness and circuits I'll go over that and report back.
There's another power distribution box under the hood by the hydroboost. The pictured diagram is in reference to this box, not the box under the dash.
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