I picked up another 86 Trooper a little while back and have been steadily fixing all the years of hack job repairs from the prior owner. I finally got around to trying to get the heater/AC working right, replaced the controls got everything adjusted up right, etc. I'm down to just a couple of problems.

#1 The A/C does not engage at all. The compressor turns over freely enough, but the clutch will not engage. Fuses all check out, no creative wiring from the prior owner, everything looks like it is in the right place, but it just won't hook up. I'm going to do some testing for power just to make sure the clutch isn't stuck or just not work, but I suspect I'll find that it just isn't getting power. It has been neglected for some years, so I assume the system needs to be recharged. So my question would be is there a cut off that keeps it from running when there isn't enough of a charge of freon in the system? I couldn't pick something like that out for sure in the wiring diagram, so I thought I'd ask if anyone has experience/ideas on the subject.

#2 The defroster door will not move at all. I tested the vac switch/solenoid deal that is in behind the glovebox and it is getting power at the right time and the vac diaphram on the other end is functional, no leaks there. My other 86 doesn't have A/C, and the setup is completely different. The defroster door is 100% mechanical, so I don't have spare parts to try swapping in and out troubleshooting. I've gone over the factory manual. but it doesn't really explain much on how this vac system works, for example where does the vac come from? Could this be related to the A/C not being functional? Any tips or ideas on how to troubleshoot this further would be a help. I have not had a lot of time to work on it, but I will have a lot more time in a couple weeks so I'd like to come at it with as many ideas as I can find.

The poor 'Zu mostly just needs a lot of little things resolved in order to bring it back from the brink of being scrap. I'd like to bring it back from the edge and get it out on the road instead of just picking it apart to fix the other one I have, which mostly just needs a new head.

Yes, there is a pressure switch that will kill the compressor if there isn't enough pressure in the system.
Also the thermostat may be bad. More likely the first is your problem.



Make sure the vacuum like is hooked up at the firewall and is bring vacuum to the solinoid. There's a little nipple sticking out right were the two A/C lines enter the firewall. That nipple should have a vacuum line attached to it. If it does and there is vacuum present, then try swapping the two hoses that go to that solinoid under the dash. They will only work in one direction and if the hoses get swapped, the vacuum operated doors won't work.

AHA! That explains that extra vac port on the intake right near the coil that had the plugged off hose running to it. Now assuming that whole setup in the cab doesn't leak vac all over the place, I should be good to go. Even if I do find leaky parts I'll know which direction to go in troubleshooting. Thank you very much for the info.

The A/C I had figured there was something to keep it from eating the compressor if lost its charge. I may just have to bite the bullet and take it in to a shop for A/C diagnosis. I have access to a lot of the equipment, but I can't discharge the system and recapture. I'd be wasting dollars trying to leak test it by just charging it over and over.

I got the line from the intake hooked back up. That lead me to a missing hose in the cab from the defrost switch to the air recirc door switch which I replaced. Then I had to swap the def switch hoses to get it working right. End result, both the defrost door and air recirculation door are working fine and no vac leaks. Thanks again for the tips.

Now all that is left is to make sure the A/C isn't screwed up by something simple before I take it in to pay someone else to tell me that.

Great! Glad to hear you got it working!