Hello all,

With the average above 90F here in Texas most of the summer, I'm looking to get the old AC system operating properly again. Currently, the heater blows very hot when temp dial is set appropriately. The AC flaps close properly producing strong air out of the center flap and when the temp dial is set to the coldest setting, the air becomes noticeably less hot.

However, my compressor fails to engage in any setting (Low,Auto,High, or defrost).

What steps can I take to test the operability of the compressor?
I'm unfamiliar with this job and I don't know if there are any hidden in-line fuses or switches which control the compressor clutch. I just want to make sure that I absolutely need a new compressor (as opposed to some wiring/electrical problem preventing its operation) before I decide to have an AC shop install a replacement and recharge the freon.

My car had set for a period of time without having the AC recharged so it likely very low. I know there is some sort of heated fail-safe to prevent the compressor from actuating when freon is low but I need to at least know what I'm dealing with (i.e. figure out if it is possible to successfully activate the compressor from the cabin electrics) meaning I need to see if the compressor clutch can successfully engage/disengage before I go tossing precious freon into a potentially inoperative AC system.

Thanks for all the help ya'll.
john.

 

This is very good, as the system seems to understand the requests given, and responds correctly.






First step is to check the system fuses. There are four of them:

1) one on the amplifer ground wire
2) one clipped to the right side of the heater case (in line, 10 amp)
3) one in the main fuse panel (#6, 35 amp)
4) one in the aux fuse panel (#16, 50 amp)

I can't remember exactly what each fuse does, but #1 is obviously OK.

If any need replacing remember the Brit rating system is higher than the Yankee system


Next step after checking fuses:


There are two wires at the compressor clutch, power and ground. The power wire is green. Turn the climate control on and simply use a test light or meter to see if 12v is being supplied.

If "yes", there's voltage on the green wire, then either

A) the compressor isn't grounded (check the other wire...is it broken?)
B) you have a compressor fault

IF "no", there's no voltage on the green wire, keep reading.....





Yes, there should be a thermal fuse, sometimes called a thermal limiter, clipped to the compressor bracket. It's square, with three spade terminals/wires.

Black wire: goes to the superheat switch at the back of the compressor
Green wire: goes to the compressor clutch
Green/brown wire: voltage supply from the climate control itself

So, the next step is to turn the system on and check for voltage on the green/brown wire. If you DO have voltage on this wire but don't have voltage on the green wire to the compressor then the thermal fuse is blown.

You can try replacing the thermal fuse but bear in mind that they normally only blow when the system is low on freon.

If you DON'T have voltage on the green/brown wire, post back. We'll have to start digging a bit deeper.


One easy thing to do is to use a jumper wire to apply 12v directly to the compressor at the green wire. The compressor should engage, even if low on freon. Don't leave it engaged, though.

Hopefully you won't hear any horrible noises which would suggest a clutch/hub failure or a serious internal failure.

Hope this gets you headed in the right direction

Cheers
DD

 

Incidentally, here's what the thermal fuse looks like

BRAND NEW OEM GM AC DELCO AC AIR CONDITIONING THERMAL LIMITER MODULE FUSE on eBay!


Cheers
DD

 

Thanks Doug for such a detailed and linear approach to this problem.

I open up my side panel to check the inline fuse after confirming the ones in the other locations mentions were operations and everything in there looked completely new as if it had never been opened or touched. The clipped inline fuse was fine as well so not a fuse problem (unfortunately).

Test light did not turn on at green wire with car on and AC activated nor did the green/brown wire at the thermal fuse (although I found it hard to test that wire in isolation because the green solid wire is bound together with the green/brown wire in a black protective coating in my car almost up to the connector with about 2-3mm of colored wire exposed).

I also ran a jumper wire from the positive terminal of the battery and touched it to the green power wire at the compressor and still the clutch did not activate.

I would greatly appreciate any further suggestions.