2 AC questions

I just bought a 2000 Cherokee a week ago. Everything is in great shape except for the three issues everybody has: valve cover gasket, AC and passenger switches. I can live with everything else for right now but I have to fix that AC ASAP! Here are my problems:

1. Occasionally when I hit a bump, the blower fan cuts out. Usually it comes right back on. Also, playing with the switch, I could make it cut out. I pulled the bezel and the box of knobs and opened it up.

Visibly it's gotten too hot (common, it seems) as the plastic is discolored. Also whatever type of grease they use for the switch was cooked in the process. I cleaned the switch and reinstalled everything.

This helped a lot but hasn't completely remedied the problem. Do I need a new switch? If so, should I go for a junkyard switch or should I buy new? Cheapest I've found is $124.78 from wholesalemopar.com - 5011343ab.

2. Occasionally the compressor clutch disengages. I jumped a wire from the battery to the hot on the compressor and it ran perfectly for about 45 minutes.

Correct me if I'm wrong, but I imagine this is the notorious low pressure switch everybody has problems with. Where is the compressor's switch located? There are 3 plugs in the immediate area. Can anyone provide me with a part number?

PS - Photos of the switch before I cleaned it.

The compressor clutch should engage and disengage periodically. Just because it disengages doesn't mean there is a problem. Does the air work good? If the charge is low, the clutch disengages due to the low pressure switch on the top of the accumulator/dryer. You can jump this switch to make the compressor run continuously to recharge, but basically it is supposed to kick in and out.

It blows good and cold, just sometimes it cuts out and starts blowing hot air. When this happens, I wait several minutes but it never comes back so I give up and roll down the windows. I doubt it's supposed to kick out that long. When I was testing, I ran a hot lead straight from the battery to it but that isn't a sustainable configuration. If you jump it to stay on, does it still kick out under heavy acceleration? If not, that doesn't seem like the best setup.

You don't want it to run continuously, but it should always be blowing cold air. Have you checked out the issue of the clutch gap? But if that was it, the clutch would click on, but the compressor shaft wouldn't turn. If you jump it to stay on, it will be on all the time. You don't want that. Supposedly, it can be the high pressure switch too. It seems like you could wait for it to cut out, and them check the switches for continuity.

Where's the high pressure switch?

I would recharge your a/c. you're prob. just low on refrigerant. Buy a can with a hose from walmart for $12 and charge it, see if that helps.

That seems to be the most common problem. The simplest solution is usually the best. When I bought my 98, the owner said the a/c was broken. A great bargaining tool for me and all it needed was a can of refrigerant and has worked perfect ever since.

Kevin108 said:

Where's the high pressure switch?

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On the high pressure line between the compressor and the condenser. It is connected electrically in series with the low pressure switch between the PCM and ground. Both the high and low pressure switches can be removed (and replaced) without freon loss, because they have schraeder valves underneath. So the high pressure switch should be closed (complete circuit) unless the pressure is too high, and the low pressure one should only be closed when there is sufficient pressure in the system.

I drove about an hour and a half in two intervals tonight with no problems. Which figures, because I ordered the new switch box this morning for $125.

Test, test, test!!!!1

I called and canceled the order. I'm going to wait and see what this silly switch does for a few more days.

Where is the sight glass on a 2001 XJ? I think I might be low on refrigerant but I don't know where to look at the sight glass to find out. And I looked under the compressor. Maybe I'm just missing it.

Where does the refrigerant go?

Something is going in and out. All day today sometimes I start it up and it blows perfectly. Other times the compressor just won't engage. The fan cutting off from bumps is completely minimized. What do you think is up with my compressor?

winterbeater said:

Does the air work good?

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It works GREAT...when it works. It's about 85° out right now and it blows so cold I had the fan on 1 and was still almost too cold.

winterbeater said:

You can jump this switch to make the compressor run continuously to recharge, but basically it is supposed to kick in and out.

Click to expand...

How does the switch on the dash control work? It has 3 contact points on the switch. Does one of them close a circuit to tell the compressor to cut on? If so, that could be my problem.

winterbeater said:

Supposedly, it can be the high pressure switch too. It seems like you could wait for it to cut out, and them check the switches for continuity.

Click to expand...

I talked to an automotive AC professional when I started having problems and he said if it was the high or low pressure switches cutting the compressor off, then they would do it when I had the compressor wired directly to the battery. I felt like the line from the battery went straight to the compressor and would be unaffected by the high and low switches, but that was just an assumption. It would make the most sense to me for the high and low switches to be in-line prior to the plug for power, but I could be wrong. I can post pictures if it would help.

If you run wires directly from the battery to the compressor, and not through the switches, the switches are bypassed and will have no effect. DUH! And I mean that to your AC "professional", not you.

The compressor is activated by a relay, which is activated by the dash switch.

When the pressure is too low, usually from not enough freon, the low pressure switch prevents the compressor clutch from cutting in. When this is the case, you have to jump the switch to get it to take the freon in. I seriously doubt that you have a low freon situation doing this because you have good cold sometimes.

The next time it cuts out, you should check both sides of the high pressure switch plug (back-probing) for 12V.

From your description, it doesn't sound like your problem is evaporator freeze up, but your statement that you get so cold that you run the fan on low, gives me second thoughts on that one. Do you know about evaporator freeze-up?

I am familiar with evaporator freeze up but I don't think that's what's happening either. Kinda strange, revving the engine occasionally seems to make the compressor kick back in. I'm going to keep my multimeter with me so I can check things right away the next time it happens.

I'm loaded up with my multimeter today. Kind of ironic hoping it messes up today.

I have proper voltage at the high and low switches. The dash switch block should be here Weds or Thurs. I'm going to put a new compressor clutch relay in tonight as a process of elimination. It's only $13.

I also bought some nice, strong alligator clips to make the bypass cable. I've got a 6 hour trip I'm leaving for Thursday night and if that switch doesn't get here, I'm not going without AC.

I really do think it's the dash switch block because the blower has been a lot more stubborn today as well.

Heat seems to play a factor. At night when it's cool, everything works great. During the day (temps have been in the 90s lately) is when things act up.

Put the new compressor clutch relay in yesterday. Everything has been 100% so far.

New switch came today. I just hooked it up and the blower quit. I'm getting sick of this fast.