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Unread 09-06-2010, 07:14 AM   #16
cruiser54
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When this happens, I would want to know immediately if there is power to the AC compressor. If there is, perhaps the AC clutch is giving up the ghost after the 30 to 40 minutes?

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Unread 09-06-2010, 08:29 AM   #17
DonMeister
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Wouldn't think so... I popped the hood to have a look when it started to warm up and the compressor was still spinning with the engine.

From your posts, I've narrowed it down to:

either an inconsistency with the low/high pressure switch from Chrysler
OR
there's moisture in the evaporator that freezes up and clogs my vents

I'll suggest these two to my mechanic and see what he says.
Thanks for all the support, is there anything else anyone can think of?
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Unread 09-06-2010, 08:34 AM   #18
1ironwill
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Quote:
Originally Posted by Weebur View Post
It sounds like your evaporator is freezing up. Chrysler has issued FSB indicating that they have recalibrated the low pressure switches that deals with this issue. There are different part numbers for the '97 and '98, your dealer should be aware of this.

Also, if your evaporator fins are dirty (clogged with hair,dirt,dust,debris) it will cause the evaporator to ice up.

Judging from the recent reposts, I would suggest the ice issue.

Last edited by 1ironwill; 09-06-2010 at 08:36 AM.. Reason: reposts before the reply
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Unread 09-06-2010, 09:42 AM   #19
irs009
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I'd bet money on your AC clutch air gap being to great. Remove the clutch (belt on, 14mm wrench) there should be 3 spacers of different thickness. Adjust (add-remove-etc) the spacers until your air gap is .018" to .031". Heat changes the air gap and I think that's whats happening.

Last edited by irs009; 09-06-2010 at 10:34 AM.. Reason: respell I'd
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Unread 09-06-2010, 10:21 AM   #20
Weebur
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Quote:
Originally Posted by DonMeister View Post
Right, so I did change the low/high pressure switch as mentioned by SubieHo... it still loses power after about an hour and a half of running. And still, after turning the car off after that period of time, I'll let it sit for a bit and come back to find a newly formed lake under the front passenger side. Garage says they'll have to keep the car for a few days to diagnose it properly.

Weebur, do you have a link for that Chrysler post?

40 degrees Celsius and 50% humidity today... ahhh
I can't remember where I saw that (it's hell getting old) but at least I did make note of the part numbers. The part number is: 05015871AA for the 1997Cherokee (05015872AA for 1998-99). Your symptoms are classic for the freeze up. I'd go to the dealer (I just gagged) for the part, the auto part stores may be selling switches that have the old calibration.

Before you lay out more cash I'd check to see how often your clutch is cycling on and off. If the clutch doesn't cycle, the frost on the evaporator doesn't get a chance to melt and builds up, restricting air flow through the evaporator. When I check my system I set up a fan right in front of the grill and blow air at it (on high). That simulates driving. And I also run the rpm's up to about 2000 for several minutes prior to and during testing.

I believe our systems should cycle about 6-10 times per minute. I count the on to on cycles.

Rapid cycling may indicate low pressure. Does hi pressure make the clutch cycle less or too little? I don't know. Obviously, too high pressure will trigger the hi pressure swich and prevent the compressor clutch from engaging. Let us know how you do, it's a common problem.

Last edited by Weebur; 09-06-2010 at 10:28 AM.. Reason: Additional Info
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Unread 09-06-2010, 10:27 AM   #21
Weebur
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Here's another thought. With the a/c on max it recirculates the interior air over and over. Once the interior air is dry the evaporator shouldn't freeze up. Are you running the a/c on max/recirculate or are you pulling in outside humid air. If you're running the a/c on recirulate and it's still freezing up I wonder if there isn't a problem with your blend doors in the box.
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Unread 09-06-2010, 11:11 AM   #22
1ironwill
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If the compressor is still spinning when the inside temp is getting warm you can narrow out the air gap, air switches (low and high side)which only send power to the compressor, and all wiring associated with the compressor, because it is still running. You can also remove the dry air, because a vehicle interior will not hold a vacuum making it "air tight". One of the problems with evaporators is the difference in temperature when running compared to ambient air. They will sweat, and why there is a drain tube attached to the housing, to remove that moisture. Even brand new vehicles will sweat.

When the freon level is low in a system it takes a good half minute for it to reequalize through the expansion valve/orifice tube allowing the pressure to drop from the high side, and build the low side back up. When this happens and the a/c is at a "on demand" setting the low pressure switch will allow the compressor to kick back on, until the compressor once again reaches the lowest attainable pressure for the freon in the system OR the low pressure side drops below the value of the factory setting of the low pressure switch, killing electrical power to the a/c clutch.

The evaporator merely is a box that functions as such. It evaporates the liquid from the condensor into a gas suitable to be compressed again. It does this by one of two functions and some vehicles a combination of both. Either 1. A smaller orifice such as a expansion valve/orifice tube or 2.AIRFLOW through the evaporator.

One of the best things about air conditioning components is that they are named for exactly what they do.

You basically can have two different problems 1. A bad thermostat saying that the evaporator is not cooling down to the requested temp allowing the evaporator to ice up or 2. A dirty or clogged evaporator.

If airflow is minimal out of the vents, I would go towards the cloggedness. At the age of the vehicle and depending upon if you smoke cigarettes, have a dog, never vacuum, it is almost certain.

Not trying to step on toes as a noob, just giving some info from ac experience.
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Unread 09-06-2010, 12:31 PM   #23
irs009
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Ironwill, You obviously know what you're talking about. My 01 XJ was spinning all of the time, even when the electromagnet was not energized. I don't know if the clutch plate was warped, or the air gap to little. Anywhoo it wound up seizing on me. These compressor clutches are temperature dependent and do strange things if the air gap is wrong. I know it's a huge leap to think that's it, and I certainly respect your superior knowledge about Auto AC.
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Unread 10-02-2010, 11:44 PM   #24
DonMeister
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Quote:
Originally Posted by 1ironwill View Post
If the compressor is still spinning when the inside temp is getting warm you can narrow out the air gap, air switches (low and high side)which only send power to the compressor, and all wiring associated with the compressor, because it is still running. You can also remove the dry air, because a vehicle interior will not hold a vacuum making it "air tight". One of the problems with evaporators is the difference in temperature when running compared to ambient air. They will sweat, and why there is a drain tube attached to the housing, to remove that moisture. Even brand new vehicles will sweat.

When the freon level is low in a system it takes a good half minute for it to reequalize through the expansion valve/orifice tube allowing the pressure to drop from the high side, and build the low side back up. When this happens and the a/c is at a "on demand" setting the low pressure switch will allow the compressor to kick back on, until the compressor once again reaches the lowest attainable pressure for the freon in the system OR the low pressure side drops below the value of the factory setting of the low pressure switch, killing electrical power to the a/c clutch.

The evaporator merely is a box that functions as such. It evaporates the liquid from the condensor into a gas suitable to be compressed again. It does this by one of two functions and some vehicles a combination of both. Either 1. A smaller orifice such as a expansion valve/orifice tube or 2.AIRFLOW through the evaporator.

One of the best things about air conditioning components is that they are named for exactly what they do.

You basically can have two different problems 1. A bad thermostat saying that the evaporator is not cooling down to the requested temp allowing the evaporator to ice up or 2. A dirty or clogged evaporator.

If airflow is minimal out of the vents, I would go towards the cloggedness. At the age of the vehicle and depending upon if you smoke cigarettes, have a dog, never vacuum, it is almost certain.

Not trying to step on toes as a noob, just giving some info from ac experience.
Great info there! I think I'm going to have a word with the guys at the shop who were supposed to "clean" my evaporator. I still have the receipt, maybe I can convince them that they didn't do it properly or they let contaminants enter the evaporator when it was out of the car.

Also, extra info, I usually run the climate controls on:

Fan: 4
Re-circulate Air
Thermostat: Blue (as far as it goes)

*sigh* To make things worse, my thermostat switch IN the Jeep on the A/C controls is causing trouble. It keeps springing itself back to the center (no blue, no red). It has done this before, but it would usually sort itself out after a few forced turns. Feels like a cable or spring is jammed or something. Any thoughts on this?

cheers guys, I'd buy every one of you a beer if I could!
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Unread 10-02-2010, 11:47 PM   #25
XGoBoomJ
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just wondering.. how do you use ac for 40 minuites? lol
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Unread 10-03-2010, 12:23 AM   #26
DonMeister
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Quote:
Originally Posted by XGoBoomJ View Post
just wondering.. how do you use ac for 40 minuites? lol
I live in the Middle-east, the temperatures are around 113 degrees the whole day and I drive about 200km a day to get to work and around...
Sure, it's possible to do it without an A/C, if you like being in a sauna for a good 5 hours a day.
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Unread 10-03-2010, 06:15 AM   #27
DonMeister
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Also, I heard a clunk as I was switching from Red (Hot) to Blue (Cold) on the AC thermostat from under the glove box. Sounded like a flap or door for some the vents didn't lock properly and now the fan's power has decreased dramatically. Arghhhhhhh WHY JEEP WHY!?!??!?!
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Unread 10-03-2010, 10:03 AM   #28
AZ Jeff
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The "thermostat" control on the heater control panel is really a control of a "blend door" in the heater box, which controls the mixing of hot and cold air streams inside the heater box.

On a 1998, the blend door is cable operated, IIRC. Look for proper blend door operation in your vehicle.
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Unread 10-09-2010, 01:20 AM   #29
DonMeister
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Ok that's it, I give up ... This thing's going into the A/C shop today. Will post their diagnosis up here within the next few days.
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Unread 10-14-2010, 07:49 AM   #30
DonMeister
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Wow... just WOW... The guys at the shop couldn't figure out what is causing my A/C to lose its coldness. They kept hinting on the cycling switch and replaced it three times, but the A/C still continues to die after 2 hours. I kept mentioning that the evaporator may be clogged, but they assured me they ran water through it and it came out the bottom, how this is possible I'm not too sure of because I thought it's a 'closed' system.

I assume they don't have the proper technical experience, at least they fixed my thermostat cable, but the heater doesn't seem to be working. They said they would have to open up the entire dashboard and clean the whole system, which is a 2-day process and will set me back around $200. Regarding the A/C, they said I should take it to the dealership (DREAD) and let the men in suits have a look at it.

I'll list the issues and symptoms one more time here for anyone suffering from the same problems:

1. A/C runs ICE cold for around 2 hours, perfectly, the way it should
2. Noticeable increase in air temperature and humidity after 2 hours of driving (regardless of highway or city)
3. Also, the car does not 'sweat' after the 2 hours. I don't see any water dripping from the passenger side (I assume something must be clogging it)
4. Fan power also decreases drastically
5. Compressor cycles AND runs properly (I checked this myself)
6. AFTER engine shutdown, give it 40 minutes or so to find a vast amount of water dripping from the passenger side

7. Once water has finished dripping, the A/C will run properly for another 2 hours, and the circle of Hell repeats

As far as I can tell, it MUST be frosting up somewhere and for some reason which I nor that one garage can figure out. C'mon lads, anyone have any experience on this matter? 1ironwill? You seem to know what you're talking about?
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