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A/C loses power after 40 minutes

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6K views 39 replies 14 participants last post by  MossGreen97 
#1 ·
Hey all,

I did a search on the forums and couldn't find anything that matches my problem. I recently sold my YJ (R.I.P. buddy) and bought myself a nice '98 XJ. Great condition and everything runs great, EXCEPT

The Air Conditioning System
Now, bear in mind, I live here in Qatar (Middle-East) and now during the summer months the temperatures are constantly 35 - 50 degrees Celsius (112 degrees Fahrenheit). An A/C here is a must.

My A/C runs fine after starting the car, blows cold air like a champ. Sometimes, the air will come out of the defrost vents when I increase the throttle. I've read up about that and have come to the conclusion that one of the vacuum hoses is old and worn out. That's not my problem though, because in the end, cold air will still come out.

My issue is: After 30 - 40 minutes of driving, regardless of highway or city, the A/C will lose power and slowly increase in temperature. The compressor is still running and while it's not warm air coming out of the vents, it not as cold as it was when I started the car. I've recently recharged the unit with R-134a gas as stated on the manual, but that didn't seem to fix the problem. I personally think it might have something to do with the plumbing system. I have a suspicion that the A/C freezes as ice builds up in the system, because, after leaving the car parked somewhere with the engine OFF for an hour or two, the A/C will blow out sweet cold air again.

Has anyone been having the same problems as me? I will probably be taking it to an A/C shop to have a mechanic look at it, but it would be nice to have a starting point or some advice from the experts at Jeep Forum.

Any ideas or suggestions are greatly appreciated! Cheers beer :cheers:
 
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#3 ·
I have the same problem.... Sometimes it will last an hour or so, sometimes 15-20 minutes... Guy at a local shop told me my A/C clutch needs re-shimmed or replaced? Taking it to them this week.
 
#5 ·
Did you evacuate the system and then recharge it will a full charge? Or did you use one of those DIY cans with the crummy gage on it?

When you let it sit, is there a large puddle of water on the ground? of course it might evaporate quickly in the heat so you may not be able to tell.

When it's blowing cold at first, do you feel a strong blast of air out the vents? Once it starts warming up, is the blast just as strong albeit warmer or does it feel weaker?
 
#6 ·
Did you evacuate the system and then recharge it will a full charge? Or did you use one of those DIY cans with the crummy gage on it?

When you let it sit, is there a large puddle of water on the ground? of course it might evaporate quickly in the heat so you may not be able to tell.

When it's blowing cold at first, do you feel a strong blast of air out the vents? Once it starts warming up, is the blast just as strong albeit warmer or does it feel weaker?
No, I didn't evacuate the system before I refilled the gas. The shop used a crummy looking can with a crummy gauge on it.

Yes, when I let it sit, there is a lake of water on the ground, it comes out as if their were a water fall built into the undercarriage.

It takes a while to start blowing cold air, maybe around 10 minutes until it's noticeably cool. The electric blower is working alright though, besides the fact that the air comes out the defrost vents at higher speeds and ONLY in 5th gear. It does get a bit weaker but only after 5th gear at 120 km/h, for a while. Sounds like the compressor clutch might be slipping or the fan belt may be loose on the compressor. We drove 80 kilometers today in 4th gear at 110 km/h @ 2400 RPM without any issues to the A/C though.

Hope that helps diagnosing it further, thanks for the feedback, cheers!
 
#8 ·
I'll give that a try as well, but again, I need to save up some money first. Then again, in a few months, the weather will be cooler here again. Until then, I could just suck it up and drive around in 4th gear at max as that seems to keep the A/C nice and cool. Thanks for the suggestions guys!
 
#11 ·
SubieHo, I've never taken a look at the A/C system myself. Where can I find the relay and how do I check it? Do I just check it through with a volt meter?

Another thing to look at is the Low pressure switch on the accumulator....mine would stick and the compressor would run non stop and freeze up the low side, and do the exact same thing you are describing, let it sit for about 15-20mins, fire it up and the air is perfectly cold, and for another 30-40 mins
Wow great. How and where do I check the low pressure switch? Must I take it to an A/C shop for that?
 
#10 ·
Another thing to look at is the Low pressure switch on the accumulator....mine would stick and the compressor would run non stop and freeze up the low side, and do the exact same thing you are describing, let it sit for about 15-20mins, fire it up and the air is perfectly cold, and for another 30-40 mins
 
#12 · (Edited)
Along the right fender and behind the battery, you'll find a relay box. Many of the relays are interchangeable. Swap another one for the AC relay to see if that fixes your problem.

As for the low/high pressure switch, jump the pigtail going into the switch and see if your compressor clutch engages.

If your compressor is running, then you should have cold air provided that you have a decent refrigerant charge.

If there's too much moisture in your system that is causing these symptoms, then you need to have the system evacuated and recharged.
 
#14 ·
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.
 
#15 ·
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
 
#20 · (Edited)
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.
 
#17 ·
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?
 
#21 ·
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.
 
#22 ·
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.
 
#24 ·
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: cheers guys, I'd buy every one of you a beer if I could!
 
#23 ·
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.
 
#27 ·
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!?!??!?!
 
#28 ·
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.
 
#30 ·
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?
 
#39 ·
I have done AC service for a living on buildings. These are the classic symptoms of freezing up. There are two issues that affect freezing up. One is too little air flow, which is not an issue in car systems. The other is under charging. This allows the refrigerant to be too cold when it enters the evaporator coil. This can be duplicated by the TXV (thermal expansion valve) being faulty. It regulates the rate that refrigerant enters the evap coil. Since you have replaced switches, I would suspect this. Have these guys hooked up gauges and checked pressures on the low and high side? That would tell them right away.

One suggestion until you get it fixed. Continue running the blower on high for a few minutes and the ice will melt while you are driving and then switch it back to AC
 
#31 ·
Guess I fooled you, ha!

Judging from the last post, its definitely freezing up. From what you said, it took longer to freeze after cleaning the evap. I would think that it is still a tiny bit dirty. Flushing with water is good, but it wont remove larger particles, such as leaves too big to fit down the drain tube. If that is not the case, then the orifice tube is clogged slightly, dropping pressure too much and the evap is doing its job, only it is not getting enough liquid into it because of the clogged orifice tube. Some vehicles the orifice tube is not removable, the whole liquid line has to be bought, unsure on an xj, but the parts stores sell only the o tube for that application, so it might be possible.

You can check for vacuum at the eng side of the firewall, then compare that reading to the back of the control unit. If the back of the control unit has the same amount of vacuum as the eng side of firewall, change the unit out first. Most of the time its the vacuum switch itself in the unit bleeding through to another side. Could be possible that the airflow going over the evap is not enough because its flowing through the defrost and not allowing the correct change of liquid to gas at the evap after longer usage which is an idea, but a remote possibility.

Does it look like a new compressor, or did you put one on? Reason I asked is there is the possibility that the po didnt know about the otube and just replaced compressor and the otube and possibly condensor is filled with compressor parts. If it looks like the original compressor, probably didnt happen.

Was the system only low on pressure before it was charged back up, or was it completely empty?
Your heater core is hooked up and not bypassed?

My experience with ac is universal, not specific to a certain model, only theory. I did work in an ac shop for 3 years, although it was only 1955-1973 vehicles of every make and model. I have other experience on my newer vehicles, and some others peoples, but havent been in the strictly ac business in awhile.
 
#32 ·
Doesn't look like they touched the compressor, looks like the original one.
Heater core is clogged... the thermostat controls are useless. I didn't really need a heater here in the desert, but does that affect the A/C ? It's a big fix according to the garage, $200 and I have to leave the car with them for two days. Or... I'll try an actual A/C shop, they've had it before and I told them to clean the evaporator a while ago, but I guess from what you've said they haven't done it properly. I'll flash the receipt at them and have a word with them
 
#33 ·
A clogged core would affect engine cooling. Yes, the dash needs to come apart. Plenty of writeups around if you feel up to it yourself.

Definately sounds like evap freeze up. You could try pulling the blower motor and having a look inside the cage and box. Never know what you'll find.
 
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