AC evaporator/erractic Opertation

Can anyone tell me how a small leak in the evaporator can cause the AC to blow cold for 20 min then stop and then back to cold 20 min later? Or is this not the cause for the erratic AC operation?

Year?

I may be freezing. The takes a while to thaw out.

Probably not the result of a leak. Symptoms of evap freeze are reduced air flow through vents. High humidity conditions cause evaporator to turn into a block of ice. The line under the hood to the evaporator will remain frosty. To reduce liklihood of evap freeze up, make sure to keep your windows closed completely and run fan on higher speeds. Use max AC mode (recirc) which reuses dehumidified air in the cabin. If you get too cold, reduce temperature knob setting instead of fan speed.

its a '01. The reason I asked is because that is what the dealer said was causing the problem and I had them fix it for 940 (sloppy work antifreeze all over the engine, carpet not back in its place, and vacuum and radiator hoses not put back in place). It didnt make sense to me but I trusted they were right because I have never had a fishy feeling about them and I dont know much about AC. Winterbeater it was the Rochester Jeep dealer.

I have the old evaporator with the die all over it. They claimed most cans of regular 134a refrigerant has die in it too which I had put in because I thought I was low on freon. Is that a true statement?

Most cans of refrigerant DO NOT have the dye in it. If you look on the shelf at Walmart (or whatever) you will see that it comes both ways. I have used quite a few cans of varied brands without dye as well as cans with the dye and have not seen any normal cans that had dye in it that didn't say it had dye. Of course dye can be poured on a part after it is removed. If the evap was leaking it should have been dripping dye out of the HVAC box condensate drain hole. Was the evap corroded? Most evaps returned to my warranty department that leaked were from corrosion (which was very visible). We tested them air under water and looked for bubbles. I don't know how one would have "dye all over it". I know it's hind site, but for others doing this, if I were ripping out the HVAC box, I'd put in a new evap and heater core at the same time.

My '00 is doing the same thing. Blew cold for about 30 minutes yesterday, then blew hot for 20 and then went back to cold.

I was on the highway at the time and was pretty sure the compressor had cut off. Was hoping to make it home so I could take a look under the hood and try probing the pressure switch(s), but then I felt a little clunk and the air got cold again. So, I figured the compressor had cut back on. Never did look into it any more...

The day before it ran for an hour w/ no problems.

The system has two pressure switches, right? A high and a low? I know one (which one I'm not sure) is right behind the compressor. Where's the other and what should I be looking for when I test them?

Thanks.

The symptoms you mention are typical for most late model XJ's. Basically there are two main things that could cause what you are experiencing...

The low pressure switch has failed, which is what is causing your evaporator to ice up. Once it ice's up, air flow is impeded, and you get the luke warm air. Once the ice melts, you get the normal cool flow until the evaporator ice's up gain about 20 minutes later. The cycle repeats. A good clue is large amounts of water under your rig...that's the melted ice. You can easily replace the low pressure switch, that is located on top of the accumluator. You can remove it without losing charge, as there is a schraeder valve that keeps your refrigerant in check...just swap in a new one.

The other reason for eractic operations could be a failed AC clutch. The AC clutch is a dealer only item, unless someone else has found another source. If you AC unit is fairly old, it would be more cost effective just to buy a new compressor, as the AC clutch will run you about half the cost (labor included) of a new compressor.

I had the same problems you did, but at 40,000 miles. First I replace the low pressure switch, and it solved the icing up problem. About a year later on my AC clutch gave up the ghost, so I chose to have the AC compressor replaced at that point rather than replace it.

I thought the high pressure switch was suppossed to prevent icing????????? You are right about the problem often being the compressor clutch, which is often a problem of the gap, which can be adjusted.

I took a look under the hood and found that the two switches look as if they are the originals. The only thing they replaced is the evaporator and it the AC now works continuously even on low. Contrary to what people have been saying it must have been the leak in the evaporator that was causing the system to stop working for a period of time. The high pressure switch is the one located near the compressor right? That switch is defiantly not new.

The high is near the compressor. The low is on the receiver/drier bottle. Hey, if it works now, why question the work that was done? The next question will be how long it works for and if that was the only leak, or if recharging the system was what fixed it.

Hey all. The new evaporator did not fix the problem. After spending a boat load of money the cold air will become luke warm in hot/humid weather when I only turn down the fan. Even a new evaporator will freeze up like and ice cube!. I know the way way to get around this from happening it to the temperature dial and mix warm air with the cold, I just thought this was wasteful and i have never had this problem until now. Is this a known problem even with perfectly functioning AC for jeeps? Will I have any recourse with the dealer i just forked 940 bucks to? Because they never fixed the problem I came in with. And of course SE Michigan has probably saw the last of hot/humid days so it will be hard for the dealer to experience the same headache.

Just hope this get to someone before they rip apart the dash or spend the money.

winterbeater said:

The high is near the compressor. The low is on the receiver/drier bottle. Hey, if it works now, why question the work that was done? The next question will be how long it works for and if that was the only leak, or if recharging the system was what fixed it.

Click to expand...

That may be true of the later jeeps, but not the old ones, the old ones have the high pressure and low pressure on the compressor, also the receiver dryer on the old ones is a high pressure area, not low. His is an '01, so you are right about his.

I think somewhere around '95 they went from an expansion valve at the fire wall and evaporator inlet to a filter-tube constant flow control part that is in the outlet of the condenser, or condenser outlet tubing. Not sure what it is called on the later models. I worked on one this weekend on a 95 ZJ.

Rather than start a new thread, I'll tack my question on here. There was another thread (that I now cannot find) that said a pressure switch can cause your AC to constantly cycle.

Is that the high pressure switch or the low pressure switch, and where are they located? I have a 97 and I'm parting a 98 (both 4.0's with auto). I want to make sure I keep the switches when I get rid of the engine and the accessories.

Low refrigerant will make it cycle.

The evaps on 97+ are notorious. I think mine just went.

drewbsking said:

Hey all. The new evaporator did not fix the problem. After spending a boat load of money the cold air will become luke warm in hot/humid weather when I only turn down the fan. Even a new evaporator will freeze up like and ice cube!. I know the way way to get around this from happening it to the temperature dial and mix warm air with the cold, I just thought this was wasteful and i have never had this problem until now. Is this a known problem even with perfectly functioning AC for jeeps? Will I have any recourse with the dealer i just forked 940 bucks to? Because they never fixed the problem I came in with. And of course SE Michigan has probably saw the last of hot/humid days so it will be hard for the dealer to experience the same headache.

Just hope this get to someone before they rip apart the dash or spend the money.

Click to expand...

If the evap really leaked (big ?), he fixed a broke part. I don't think you have any recourse. Keep the windows closed, run MAX AC to keep it in recirculation mode, and keep fan speeds up to minimize icing. I've seen new Durangoes where everything was replaced and the problem still persisted. I think the guy was a smoker (vehicle was rank inside), who maybe liked to keep his window cracked open.

Just wanted to follow up on the the thread I started. The evaporator was leaking and was replaced but it did not fix the the problem of the AC working for a period then becoming luke warm. The dealer free of charge replaced the orfice valve which in fixed the problem for good. For those who evac the system replace that piece of tube. Although i dont know how much it cost. But from my knowledge its nothing other than a tube with a narrowed down across a screen so it should be cheap. Anyone know how much this part is?