The A/C in my Jimmy hasn't worked for years, but my wife hounded me enough to take a look. When I turn on the engine and switch on the A/C, the compressor clutch doesn't engage. I ran a wire from the battery to the compressor clutch with engine off, key on, and the clutch will engage using that method. My question is if there are any other fuses/relays that I need to know about besides the relay in the engine compartment fuse block. I swapped the horn and A/C relays in there in since they are the same, still no go. In the Haynes book, there are relays pictured on page 6-12 (figure 4.53), but my Jimmy does not have this set of three relays, It has one, and Haynes neglects to mention this. Is this one relay A/C related, or is it just for the blower motor? What should my next step be? Test the switch?

By the way, I did test the compressor clutch connector, and couldn't seem to find any voltage there.

Here's the one relay I was talking about:

 

Your compressor will not engage if the R134a refrigerant is low. That is usually the most common cause. This is a safety thing so the compressor doesn't run with low refrigerant as it will damage the compressor. You should check the refrigerant level and hi/low pressures before anything else. Let us know what you find out.

 

Thanks for your reply! I will do that. Should I assume that there is a leak in the system if the charge is low? From what I've read, the compressor must be running when recharging the system. Is it okay to recharge if the compressor is not running due to the low pressure switch. And also, can you point out the low pressure port for me? Thanks again!!

 

The low pressure port is on the accumulator (Silver can) with the black cap on port cover. You can temporarily bypass the low pressure switch (also on the accumulator, opposite side from the port) by pulling the wiring harness and using a paper clip in the harness to engage the compressor. Only do this if you are recharging, don't run the compressor otherwise.

You should probably look at having you A/C system evacuated by an A/C tech. You mentioned that it hasn't run for years......you most likely will have moisture n your A/C system and that can really cause problems. Moisture will freeze and block the flow of r134a. That is what the accumulator is for. It has a desiccant inside to absorb moisture but they do wear out. Cheap to replace though, they usually run about 15-20 bucks for anew accumulator.

Oh and yes, you should assume you have a leak if the r134a is low. Auto stores do sell r134a with dye that will show up where it leaks (if it's at a spot thats easy to see)....check it out at a parts store. Usually the dye is kind of a fluorescent green color.

However you may have a really small leak and recharging may get you by for another season. Let us know what you find out!

 

Yeah, from what I have been reading elsewhere, I figured I was going to have to take it to someone for the recharge since it hasn't been run for so long. Sucks, lately I've been trying to tackle some repairs myself that I've put off for awhile since I was too lazy to bring it to someone. I'll probably be on here some more. Thank you again.

We were posting at the same time. Since there is a chance that there's moisture in the system, I'll have an expert take a look.

 

Yea, I hear ya. The one big obstacle for A/C do-it -yourselfers is having a vacuum pump system to evacuate the A/C. It's one of those expensive tools that you might only use once.

You might still try jumping the low pressure switch for a few seconds just to see if the compressor engages.... that should verify that you are low on refrigerant and not something else.

 

I will try to do this before it gets dark. You said to only do it if I was recharging. Could I harm the system by jumping the low pressure switch for just a quick moment, just to see if that is the reason that the compressor isn't working? I didn't buy any R-134a yet since I wanted to see why the compressor wasn't running.

 

It will be OK for a few seconds. Jump the low pressure harness with a paper clip or something similar, start the engine and turn the A/C on. Go check to see if the compressor is running then go shut it off. I wouldn't let the compressor run like that for too long unless you are recharging it. Let us know....

 

Jumping the low pressure switch is how you get the compressor to take a suction of off the can of freon. Once it has a little pressure you can remove the jumper. That said if the system has no pressure at all then you need to pull a vacumn first in order to remove all the moistrure from the system. If you have leaks you would want to get them fixed first as well.

 

Sorry, two more questions, then I'll leave you alone. You mentioned there is probably moisture in the system. So I probably shouldn't even bother trying to recharge unless I get that accumulator replaced, right? And also once I get a shop to evacuate the system, is the accumulator the only thing that I should replace that may have moisture? I will also have to check for the leaks.