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  #1  
Old June 22nd, 2011, 21:03
Magus2727 Magus2727 is offline
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Diagnose AC system? Low pressure good, not so much on High pressure

I am having AC problems. The Jeep has always had AC problems since I have owned it and I have always in the passed looked only at the low pressure side. The jeep has been acting up more so lately so last week I added a small can of recharge to the system. It did not do anything if anything it made the problem worse.

The Problem: The AC will work (normally) the AC compressor's clutch operates fine and I get cold air out the vents. at idle I can hear the aux fan turn on and the engine idle lowers due to more load on the engine. however after some undetermined length of time (varies) i will start to get warm air out the vents. I have pulled over and checked under the hood to see whats going on and the clutch does not engage. If I turn the AC off and go to vents only for once again an undetermined length of time I can then go back to the AC and it will start working.

Well Summer was coming so to try to fix this (often AC compressor not engaging is due to low pressure on the low pressure line, so i am told) I added a small can of 134a+. It helped a little (made it colder) but has made the working of the AC even more unpredictable, and even get a odd noise from the fan (I think the fan bearing is just going out and make a noise when its cold). And sometimes now the AC aux fan will stay on even when the compressor is off and does not turn back on.

Well I was dying in my jeep in the 85* weather today and its getting even hotter. so I stopped by a part store and picked up a EXChill Manifold gauge and hose set that measures low pressure and high pressure to see a better picture.

The kit came with a diagnose chart when certain conditions are met, however it did not have my condition. I have good pressure on the low pressure line. It was at 35 psi, its about 70-75* in the garage (door was open) and engine had been sitting for about 2.5 hours prior to testing. the jeep was set at MAX AC with max blower speed. The high side read 350 to 375 psi which per the dial says "ALERT" and the chart for temp says i should be around 150 to 180 psi. The Air was cold and it sat there so I waited a few min to see what it did. it stayed. the AC clutch and aux fan stayed on and engaged the entire time (no cycling). this had me worried a little bit.

After a few min every thing was still at the above pressures so I assumed it was steady state, perhaps it was not cycling because to conditions or being on MAX so I turned the climate control to normal AC and the pressure went up to 400 psi this is in the "NEED SERVICE" section. it stayed at 400 psi on the high side and the clutch continued along with the fan not to dis-engage. I turned it back to MAX AC a few min later and it stayed at the 400 psi on the high side. All the time the low side is sitting right at 35 psi. Then the high side pressure fit coupler, from the gauge set, popped off the port on the high pressure side.

Sorry for the long story, I wanted to give as much detail and things I have already covered before asking some questions.

First, what would be the case of having "normal" pressure on the low line but way high pressure on the high line?

Second what would cause the AC clutch engagement to act the way it is? Since the Fan stays on or off (usually) the clutch should be fine right? it would seam like what ever is controlling them is acting up? Should I Evac the system and replace the pressure switch and re-charge and see what happens?

This is driving me crazy, and the wife is due next month and the Jeep is the DD, so it will not be happy for anyone unless I can get the AC worked out.

Thanks in advanced to the help and suggestions, and for also getting this far in reading my short essay.
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  #2  
Old June 22nd, 2011, 21:10
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

If the system is over charged, it will shut down when the pressure builds up. That is why you measure before you fill. Sounds like it is over filled.
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  #3  
Old June 22nd, 2011, 21:13
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

?? The system never did shut down, it stayed on the whole time. the AC clutch and aux fan was on the entire time the jeep AC was on. the low line is nominal, the high side is to high.

When I filled I used a single gauge on low line and it was always "nominal" when I filled
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Old June 22nd, 2011, 21:35
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Take it somewhere that can evacuate the whole system, pull vacuum and then charge it with the correct amount of refrigerant. I bet you find the problems gone after that.

Like Old Man said, it sounds like it could be overcharged. Since you have been adding a can here, and adding a can there you don't really know whats in the system. Most shops around here won't charge more than $50 to do this. If you hate the heat as bad as I do it might be worth it.
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Old June 23rd, 2011, 04:45
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Thanks, Does any one know how much it usually costs to replace the pressure cycle switch while they are evacuating the system? I would hate to do all this and find out I need to evac again to replace that switch.
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  #6  
Old June 23rd, 2011, 05:00
thebrick thebrick is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Might want to check the specs on the air gap on the AC magnetic clutch...

check this out:

http://www.askamechanic.info/askamec...nt/view/73/47/
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  #7  
Old June 23rd, 2011, 05:09
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Thanks, I will have to sit down and read the link... on my way out the door right now...
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Old June 23rd, 2011, 05:53
thebrick thebrick is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Actually, reading over your initial thread again...sounds like you've got a blockage somewhere in the expansion valve, maybe too much oil and/or bad compressor.

As other have stated, it might be best to take it to a professional...

Not sure about the pre 97 XJs, but on my '00, the compress has a pressure relief valve...it once got to much oil and 'spit' it out into the engine bay...it was nasty...it was green!
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Old June 24th, 2011, 18:31
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Arg, token expired? I wrote this good post about my AC and need to do it again..... well...

Took my Jeep into a shop today first thing in the morning, and they hooked it up to the AC machine and they measured pressures and they evacuated the AC and did a few other tests and refilled. they did not say anything about 400 psi on the high side and I came in full so they did not charge. the shop said the problem was because I was missing part of my shroud for the mechanical fan (the top part).

I went to the dealership and picked up a new one and installed it. I had installed a new one a few years back and I remember needing to take the fan off to install it for the clearances, but this one just slipped in with the fan in and was easy to install, because of my new motor mounts?? o well....

Driving along and things seam alright but the AC stops working again same story, AC clutch not engaging and the AUX fan running. even with the new shroud which was "suppose" to be the problem. No harm done I needed a new one any way for the last year so it motivated me to get it sooner.

I took the Jeep back into the shop and left it running so they could see that the clutch was not engaging. I had been driving it for about 10 min and then it sat idle before them pulling it to the shop for another 20 min or so all the while with the AUX fan on and the AC clutch not running. Get into the shop and the pressures look fine and the Mechanical pulled out a little light and started moving some wires and it "magically" turned on (I use quotes as you will find later one). we tried moving what wires we thought he moved when it started working but the AC continued to run and no amount of revving or such would turn it off. So I thought who knows, perhaps there is a bad connection and like most electrical problems they don't usually play nice in finding the problem so this might have fixed it. bad connection or something that just was positioned in just a way to cause problems. I drove off not more than 1/4 mile and the AC cut off.

I brought it back and left it on again, this time it was idle for I would say 45 min or so (perhaps longer, it felt really long). They once again hooked it up to the AC unit and everything ready fine. they looked at the low pressure switch and it was only giving 11V out, when 12V was applied the clutch kicked on and worked. So they evacuated the system and took the switch out and cleaned it up. installed it again, recharged the system and all is working well. they did a bunch of restarts and revving and it worked.

Drove it home worked well got nice cold air. went out to dinner and mid way started blowing warm/hot air again, got to the restaurant and left the Jeep idle and popped the hood, AC clutch not engaging but the AUX fan going.

So I called up the shop and he is ordering a new low pressure switch in and will hopefully be able to install it tomorrow at some time and the AC problem will be solved... if its that easy.

So far I have liked the shop I have gone to (first time) and they have not charged me anything (even with me offering). Fingers crossed, and I will update.
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  #10  
Old June 24th, 2011, 19:15
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

If you find a good shop, don't forget to pass the name around. They are few and far between.
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  #11  
Old June 24th, 2011, 19:29
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

I was after everything goes down... its a fairly new shop.. I figured the local area would be the best place to post since it be more relevant to those who look there.
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Old June 25th, 2011, 15:16
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Well they replaced the low side pressure switch... still does not work the way it should. I just checked the clutch gap (or at least I think I did) and measure 0.028" and its within the recommended distance per the FSM. Top measure the gap you measure between the pulley and the clutch right? there are "two" channels 1 right along the very edge of the clutch which is wider than the one closer to the center of the clutch. the smaller channel i was able to fit a 0.012" combined with a 0.016" feeler gauge into the smaller channel.

is that the right gap to measure?
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Old June 25th, 2011, 17:10
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

* edit .. sorry gave irrelevant advice

Is the clutch getting signal when it stops working?

Last edited by ktwalker01; June 25th, 2011 at 17:14.
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Old June 25th, 2011, 17:30
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Quote:
Originally Posted by Magus2727 View Post
Well they replaced the low side pressure switch... still does not work the way it should. I just checked the clutch gap (or at least I think I did) and measure 0.028" and its within the recommended distance per the FSM. Top measure the gap you measure between the pulley and the clutch right? there are "two" channels 1 right along the very edge of the clutch which is wider than the one closer to the center of the clutch. the smaller channel i was able to fit a 0.012" combined with a 0.016" feeler gauge into the smaller channel.

is that the right gap to measure?
I'm not following this....the low side pressure was fine so they replaced the low side pressure switch? If the high side pressure is bad, why would you replace the low side switch.
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Old June 26th, 2011, 14:17
Magus2727 Magus2727 is offline
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Re: Diagnose AC system? Low pressure good, not so much on High pressure

Apparently when hooked up to the shop machine the pressure levels on the high side and low side are nominal. There are no "pressure" problems. The low pressure switch was replaced because the mechanic only read 11 volts out of it when it should be on. When he "jummpered" 12 volts onto the line the clutch engaged. So the thought was that the sensor was bad (to much of a voltage drop through it??). That is why the low side pressure switch was replaced.

The low pressure switch (in reading the above link and looking at the schematics) the low pressure switch is what directly controlls the clutch engagement right? Where do you measure at the clutch? There is a ground cable on the housing of the compressor but the other lead goes right into the pully and is sleeved the whole way. Guess I can remove the wireharnes connector and measure there...

I have not tried the "bumping" method but the gap I think is a good distance...

Thanks for all the help thus far!!
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