What is this connection for
 

I recently just purchased a pretty decent 1990 gmc k2500. And I'm trying to fix my a/c system.

Trying to figure out what this green connection is for on the back of the ac compressor? And where the wire that use to go to it, might be routed. This is the third motor that has been placed onto the vehicle, and it's hard to know what is missing.

Re: What is this connection for
 

That is the ac high pressure cutout switch, one wire. Maybe a green wire with black connector. It’s bundled in the engine wiring harness.

Re: What is this connection for
 

Thanks for the reply. Unfortunately I spent the evening looking for that wire but could not find it. I opened up most of the looms hoping it was folded over in one of them but never found it. My AC is running, but I'm not sure it's good to use it without that wire hooked up?

Re: What is this connection for
 

No expert but lots of older cars never had a high pressure switch. I am not sure if my 93 does either. I just check it with the gauges, with it working and as long as they are right I don't think I would worry to much about. It shouldn't be had to add one in the circuit though.

Re: What is this connection for
 

1990 would've been setup for R12 refrigerant. It wouldn't have the wiring for the high pressure cutoff switch. You can look at the wiring diagrams to be sure tho.

That compressor is for an early R134a vehicle 1995 ish. GM stopped using the Harrison R4 compressor after 97 or 98 or so.

Re: What is this connection for
 

Thanks for all the replies. You can't see it in the picture. But that yellow tag, says caution r12 refrigerant under high pressure. I went on ebay and got a few cans of r12 and charged the system. and got it working, the compressor seems to cycle on and off continously, with no break. kind of bothering because you can feel a huge lag on the engine at highway speed.

Re: What is this connection for
 

I assume you pulled a vacuum on the system to check for leaks before charging it up.
Just filling it up when the system has leaked out and filled with air is not good for your compressor.

Cycling on and off could be several issues.
Put a gauge set on it and make sure you have a full charge and haven't overfilled the system.

Re: What is this connection for
 

No I didn't. The system still was holding pressure and working kind of. Slighty cold air would blow when the ac was turned on. What your suggesting would have been the proper thing to do. I should maybe start a new thread, with the back story since I did figure out what that connection is for.

Re: What is this connection for
 

Whether you start a new thread or just continue this one it sounds like it would be good info to have. BTW, howdy neighbor.