Check the air gap with a feeler gauge. You would need pressure gauges hooked up both the high and low service ports. Why didn’t you have voltage to the compressor? Because the low pressure switch prevents the clutch from engaging if there is a problem.

what exactly did you jump?

Put a jumper wire across the low pressure switch (harness) terminals.

I'm just trying to verify that's what the OP did.

I jumped the plug that goes on the drier by the vacuum reservoir. The clutch engaged. I’ll have to go buy a feeler gauge I don’t think I have one.

So that tells me either the switch is bad (unlikely) or you're low/out of refrigerant...you have to put gauges on it to tell if it's the latter.

When you mentioned the accumulator is that the large round black cylinder thing with two pipes coming out of it ?
thanks

R-12 systems only have a low pressure switch so that is the only one he could have jumped


Yes. Accumulator; receiver/drier
https://cimg0.ibsrv.net/gimg/www.for...8086359dc.jpeg

Ok thankyou ..

The OP stated: "With the blower motor on low and the ac switch turned on the climate control panel it has power 10-11v. And when I jumped it the clutch engaged." ...from this context the "it" could have been the ac switch in the control panel, that's why I asked for clarification.

I’ve been thinking about it. I noticed the plug on top of the ac compressor the clip is broken. It made me thing is there any sort of wiring that’s screwed up I can check that will cause it to not turn on?
Is there a loaner gauge for r12 ac systems so I can check the pressure?

Im gonna do that to. I need to finish up my problem with the water pump bolt. Then im gonna move onto AC most likely. As 100+ degree weather is on its way in a few months.Do they still loan gauges for R12 ac systems?

my local O'reilly does

Ok, ill loan some of those. And do I connect it to the low side which I think is the blue cap on the Ac dryer. And the high side the black cap next to radiator and radiator reservoir? Or is the high and low side something else?

You stated in post #20 that you jumped the terminals at the low pressure switch and the clutch engaged. The clutch wouldn’t engage if there was a problem with the wiring, so I’d recommend focusing on the charge level of the system.

Also, are you certain it still uses R-12? I know it’s not impossible but it seems unlikely that a 35 year old truck hasn’t had any AC service.

Do not rely on the under hood label for the type of refrigerant it’s using - the system could’ve been converted and a new label was never applied.

If you’re unsure, post a picture of the high and low side service valves - it’s easy to tell if the conversion has been done by the valves.