Rotorhead

I have been having this issue for about a year now. 97 XJ.


My a/c is randomly blowing warm air. It works fine the majority of time and blows ice cold, but recently the problem is becoming more common. It always blows cold at first start up. And it never starts blowing warm air until it has warmed up.

I have purchased one of those a/c charge pro kits and when I hooked it up, the pressure was in the green, but I moved the needle to the top of the green just for the sake of it.

I pulled over yesterday when the problem occurred and the compressor was not spinning at all.

The strangest part of the whole deal is that if you keep driving, it will eventually start blowing cold air again. Sometimes after a few minutes.


Thoughts? Ideas?

Bugout4x4

Sound like the high pressure switch is bad or it is slightly over filled. As you start driving it the pressure increases. The high pressure switch shuts the compressor off until the pressure returns back down to an acceptable pressure. Either of the two causes above will make it cycle on and off like you are describing. It should be hooked to a real set of gauges and checked by an A/C tech.

Rotorhead

The high pressure switch is on the back of the compressor right? How does it work? High pressure allows voltage to pass from one terminal of the connector to the other and kill the compressor? Or High pressure interrupts the voltage between terminals on the connector and kills the compressor?

I want to test this while it is actively giving me issues to see if this is indeed the problem. Need to know if I should pull the connector off while it is acting up (which I have done and nothing happened) or if I should pull the connector off and jump the wires while the problem is occuring.

Bugout4x4

Correct, it is behind the compressor hanging down out of the line that runs up to the condenser, the low pressure switch is out of the top of the dryer canister on the firewall. Power comes from the A/C switch and runs through both the low and high pressure switches on it's way to the compressor. If one or the other detects high or low pressure it opens the circuit to the Compressor.


I am not going to suggest jumping it to test, that is on you if you want to try but you do not want to run it that way. But if the switch is bad you will have to take it to a tech anyways. It will need to be properly recovered changed out and then refilled with the proper equipment. In warmer climates it is very important that it is brought down to a proper vacuum before recharging.


Side note: Notice how they built the high and low lines as one assembly where it bolts to the compressor? I would once again like to reiterate how much I hate Automotive Engineers. My high side line just went bad.

Rotorhead

I should clarify that I do not plan to jump it and run it that way. I'm only going to jump it quick to see if the compressor kicks back on while I'm having the issue to confirm that is where the problem lies and then proceed from there.

I thought the switches had some sort of schrader valve to keep from having to evac the system and then recharge?

Bugout4x4

Looking at either switch you will notice they screw into a threaded port like a pipe plug. The only Schrader valves are in the separate high side low side connections to charge or monitor pressures. The system has to be evacuated to change these switches. But it may not even be a bad switch. You need to put a real set of gauges on it and know what you are doing to make sure it isn't just an over charge issue first. It may not have been brought down to a proper vacuum the last time it was charged, This would also cause a high side pressure issue that can only be detected with a proper gauge hooked to the high side.

Rotorhead

Okay so I did a bit of trouble shooting on this today. I just let the jeep idle for probably 20 minutes or so with the a/c on full blast.

At first I couldn't replicate my problem. The a/c wouldn't kick off at all, had good drainage of the condensation. Then I started throwing switches around. Moving the blower settings around, turning the a/c on and off a bunch of times. Eventually the compressor stopped turning and the air began to get warm. I unplugged the connector on the high pressure switch near the compressor and as soon as I unplugged it, the engine revs died down a bit. Then I used a jumper wire in the connector to complete the circuit. The revs immediately jumped up just a bit like they were before I had pulled the connector off, but the compressor didn't spin.

Then I pulled off the connector on the low pressure switch. Same thing happened. Engine revs dropped off a bit. Then I jumped the connector with a wire, and again, engine revs came back up but the compressor didn't start spinning.

So It appears that both the high and low pressure switches are working correctly, as you can hear an audible change in the engine rpm that you normally hear when you turn the a/c on, and when either switch is disconnected, the revs fall to where they normally are when the a/c is off.

I also swapped relays in the fuse box. I moved the relay marked for ABS and switched it out with the relay marked a/c clutch. No change in compressor behavior.



I've been doing a bit of reading and it like a lot of people with the same issues as mine are removing shims from the a/c clutch and having good results.

Bugout4x4

I tried to figure out how the Clutch could do this? did they explain what is happening to the clutch and making it do this and why removing shims cures it?


The clutch is engaged by an electromagnet and only all in or all out when the circuit is closed or open. Maybe the shaft is expanding from heat and getting longer making the clutch slip? Maybe the electromagnetic field is getting weaker due to heat? Honestly never seen either, but anything is possible I guess. maybe the windings are heating up and breaking contact? The later would not happen in a regular cycle though.


I can't help thinking that if the clutch is indeed slipping at any point it would make some sort of whine or grinding sound. I'm thinking that if you do not hear a whine or slight grinding noise from the clutch when it is doing this then it is probably not a shim issue.


Sure wish I could talk you into hooking up a set of proper gauges before you go to all that work pulling the clutch apart and playing with shims.


Try this...Get a cheap test light if you do not have one and poke the wire that goes to the clutch right on the compressor when it is acting up. it you have no juice It is not the clutch, it is a power management issue for sure. If it has juice then it very well could be a clutch issue of some sort.


Thanks for the update!

Rotorhead

After some reading, its actually pretty common with the compressor in the xj. Basically the clutch is worn down enough that the magnet can no longer engage it, so you need to pull the clutch closer to the magnet so it can grab again.

Bugout4x4

I have seen this just a couple times on other makes. But usually the Clutch plates are fried from slipping too often by the time it gets to me. You may have caught it in time

snozberries

Mine was having intermittent AC issues when I got it as well. Ended up removing a shim and it's been working fine ever since!