So this summer my a/c quit blowing cold air. I've dealt with it because the Jeep is not a dd. Its a 99 Cherokee sport. I know the system is not leaking. My friend who is an ac tech put gauges on the system and according to him both high and low side pressures are correct. The compressor will not kick on though. I jumped the low pressure switch, and still nothing. I'm not sure if it could just be the switch in the cab not telling the system to kick on or what. When I jump the compressor from the ac relay under the hood it will kick on and blow nice ice cold air. Where is the vacuum switch that changes vacuum to electricity to go to the pressure switches? I am at a loss. Any suggestions would be much welcome. Thanks guys and gals. Scott

 

i'm not an a/c tech but i know you can't check hi/lo pressures if the compressor isn't engaging. the pressure will equalize when the compressor is not in use. but it sounds like you have an electrical problem. does it engage when you select defrost?

 

Step 1: buy a test light or dvom

If you can jump the relay, and everything functions normally, then the compressor and r134 charge is fine. Relay will more than likely have 4 or 5 prongs. Constant power, constant ground, switched power/ground (which would be the signal coming from the control unit) and then your last prong is your power/ground to energize the ac clutch.

Make sure you have good power and ground, then make sure you have a signal coming from the control unit. If you have those three and it still wont engage, its probably a bad relay.

 

Correct, you can tell if there is actually freon in the system, but there is no way to know how much.

 

I agree that you can not check the pressure's with the compressor not running, but I can jump the compressor from the relay and it will run.

 

I'm no real help. Just reminding or pointing out, on my 90 it engages now and then on it's own, presumably to keep it in shape, work the seals. I assume the pcu does this. I would guess it's grounding the relay to do it. I'm not sure, but the vacuume might be just to work the vents, and it may have a switch in the AC control. Maybe.

 

I believe you're correct... there is a low pressure switch... hats the wildcard once you've checked everything else

 

Hey Slick, welcome back.
Sooo then. Is that a relay he can just switch with another there to check...things?

 

It's not so easy to get to. I believe its in the housing under passenger dash. There are ways to test it but you have to know what your doing. I was activating relays and basically mapping out the whole system. I was trying to figure why mine didn't work. Turned out the switch was just doing its job.

 

Sounds messy. You do it, I'll have a doughnut.
???Turned out the switch was just doing its job. ???? U saying you just hadn't turned it on?

 

Naw... had no pressure in the system. It was when I just got the jeep and was still gettin to know her