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Unread 10-15-2010, 05:41 PM   #31
1ironwill
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1996 ZJ 
 
Join Date: Aug 2010
Location: tampa
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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.

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Unread 10-15-2010, 11:46 PM   #32
DonMeister
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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
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Unread 10-16-2010, 08:37 AM   #33
Saudade
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Quote:
Originally Posted by DonMeister View Post
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
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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Unread 10-16-2010, 11:20 AM   #34
1ironwill
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Try the flushing of the evap first, as you stated, once that happened it went longer. I am not sure if the heater core being bypassed would have anything to do with the airflow, but I kinda doubt it because of a vent setting. The only thing I was thinking about there was that the fan blew through the core before the blend door and then the evap, but that wouldnt make sense if it was just pulling in outside air. It wouldnt be feasible to blow outside air over the core before it got blended. Disregard that thought.

I agree on the fan blower removal. Easy enough task to get a possible peek at the evap fins. Another possible peek would be at the fan blower resistor as most commonly those are before the evap also. Not as large of a hole, but might gain a peek anyways. I do recommend taking it to a ac only shop. That way they can see what the high side is doing also. I would suggest the dirty fins again saying that it did last longer, but still is freezing up suggesting they are still dirty enough to cause that problem. I would take the blower out and look around first to see for myself.
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Unread 10-16-2010, 11:23 AM   #35
Saudade
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The fan always blows air through the evap, then past the blend door. The blend door will then direct the airflow through or around the heater core.
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Unread 10-16-2010, 12:42 PM   #36
tjwalker
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Good advice above; this sounds like it really could be the low pressure switch problem. I had it on my 99 as well. A new switch for about $20 completely cured the problem.

Here you go.....


A/C Evaporator - Freeze Up
Notes
Number: 24-13-99
Group: Heating & A/C
Date: July 2, 1999
SUBJECT:
A/C Evaporator Freeze Up

OVERVIEW:
This bulletin involves installing a revised low pressure cycling switch.

MODELS:
1997 - 1999 (TJ) Wrangler
1997 - 1999 (XJ) Cherokee

SYMPTOM/CONDITION:
Intermittent low A/C output due to reduced airflow through the evaporator or excessive condensation draining from the vehicle after the vehicle has been turned off due to evaporator freeze up. The system will operate normally in most conditions. The condition will only occur after extended periods of driving with the A/C system operating. The system will return to normal operation after the NC system has been turned off long enough for the ice on the evaporator to melt.
DIAGNOSIS:
If customers complain of this condition and no other NC system problems are found, perform the Repair Procedure.
PARTS REQUIRED:
1 05015871AA Low Pressure Cycling Switch (1997 Models) 1 05015872AA Low Pressure Cycling Switch (1998 - 1999 Models)

REPAIR PROCEDURE:
THIS REPAIR IS COMPATIBLE WITH DAIMLERCHRYSLER'S MOBILE SERVICE PROGRAM AND DOES NOT REQUIRE HOISTS OR OTHER FULL SERVICE FACILITY SPECIAL EQUIPMENT.

1. Disconnect and isolate the negative battery cable.

2. Disconnect the low-pressure cycling switch connector from the low pressure cycling switch located on accumulator.

3. Remove the switch from the accumulator and remove the 0-ring.

4. Lubricate the 0-ring with refrigerant oil and transfer it to the new switch. Install the new switch. The switch should be hand tightened to the accumulator fitting.

5. Connect the harness to the switch.

6. Connect the negative battery cable.

TIME ALLOWANCE:
Labor Operation No: 24-35-35-90 0.2 Hrs.
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Unread 10-17-2010, 06:21 AM   #37
Weebur
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I'll state the obvious. The right thing to do is pull the dash (yes, it's a PITA), replace the evporator/heater core/accumulator/orifice tube/O-rings/evacuate and recharge and replace the low pressure switch with a recalibrated unit, and be sure to replace the foam gasket between the HVAC box and the inside surface of the firewall. Mine was shot and allowed all kinds of debris to get into the box. I used high density/closed cell foam.

Have you tried shutting down the AC and opening the windows every 30 minutes or so? This might let the ice melt on the evaporator before it gets completely plugged up.
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Unread 10-17-2010, 08:32 AM   #38
cruiser54
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I think I'd be going for the $20 fix as described in the TSB that tjwalker provided.
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Unread 10-17-2010, 10:02 AM   #39
ChicoXJ
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Quote:
Originally Posted by DonMeister View Post
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?
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
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Unread 10-18-2010, 12:59 PM   #40
MossGreen97
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tjwalker's post of the TSB should be all the info you need. Had this same problem on mine back in 1999. Dealer repair, Low pressure switch change out.
If you are getting good airflow, the evaporator is not clogged. If the low pressure switch(which cuts the compressor off at a certain pressure corresponding to 34 degrees F. to prevent freeze up) is not working , the compressor will continue to lower the pressure and therefore the the temperature of the refigerant. Once it get below 32 degrees F., the condensation on the evaporator will freeze and block the air flow. This ice block will then melt with the a/c off leaving a nice size puddle of water.
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