TJ A/C Issues

You may have an incompetent repairman. Ice anywhere on an A/C system is solid evidence of malfunction.

Replacing hoses to fix icing?!?!?! Who swindled you on that?

A refrigerant undercharge is (paradoxically) one cause of icing. An undercharge will also behave as you describe, working OK in light loads, but not keeping up with more heat and/or humidity. So will a restriction in the system.

Why was the low-pressure switch replaced? More guessing at your expense?

When you have the evaporator and accumulator replaced, you should have demanded a vacuum leak test, where you actually personally get to watch the gages and see them hold a vacuum. So many A/C techs are incompetent or will wave off a slow leak because they make believe it is fixed or won't matter.

If you've paid as much as I think you have for this work, then you should have been shown performance test results per the service manual. None of this wave-of-the-hand-your-done.

A/C work is absolutely the worst to hire out. Huge prices for guys who pretend to know something they don't. That's why I learned to do it all myself.

First, thanks for the rapid reply. All of those repairs were done in one fell swoop as a comprehensive repair to stop the system from freezing up, and subsequently, restricting air flow through the vents, especially after being at highway speeds for more than a few minutes. This shop has always been competent in other repairs, but this A/C is seemingly giving them a lot of trouble. Since, as you guessed, I did end up paying a decent amount for it all, I'm bringing the car back in for a third time to hopefully get it completely fixed. I will demand to see the results of the vacuum test to make sure there are no leaks, and also make sure their charge is adequate. Hopefully this debacle will finally end. Thanks again. Joe

Should have had a comprehensive diagnosis before the comprehensive repair.

Sounds like a WAG to me.

Quite true. Even a truism. But how often wishful-thinking replaces solid diagnosis.

Just curious, could any of those replaced components (evaporator, accumulator, etc.) been damaged by a chronic undercharge of the system (excessive and constant freezing up of system for probably 2 years)? I try to keep my car in nearly perfect condition, and this issue was misdiagnosed so many times that it persisted as the freezing problem continued for quite a while. I just want to make sure those parts were not compromised *because* the shop dismissed the problems for so long, in which case, making the responsible for their failure. Thanks again. Joe

On Sat, 16 Jun 2007 03:07:44 -0000, Joe wrote:

One thing that can help A/C output overall is to shutoff water flow to heater core in summer (Lowes sells some in line ball valves that do nicely when adapted to this here) The reason for this is not most car simply try to route air around heater core in hot weather but the 200 plus cores is still in there on a hot day radiating heat into ducts. This is why when you shut your car off on a hot day for a while and then start it up it blows hot air for a while from A/C vents because the hot core heat soaks the whole A/C and heater box when you shut it down. I have done this to all my SUV's. It helps the air be a bit cold overall as well because the ducts doors and such leak with age and shutting off the hot water cures this leakage for good. You will notice first time you hot start it after it sits for a bit that there will be no blast of hot air from vents for heater core cooking ducts and A/C will work better in recirculate mode too because there will be no hot spots in the ductwork to warm air and full capacity will go to cooling car. I can run my truck in 90 plus weather, blowing snow flakes so to speak, stop for a while and then start it back up and no heat soaked blast and have full cooling in a matter of seconds. You may have some other issues but it kinda sounds to me the you may have some heater door leakage and heat soak because the hotter it gets the hotter the coolant is going to tend to get and the more it is going to warm your air in ducts. Long ago they used to shut water flow off on a lot of vehcile when heat was not on and A/C was selected but to save prodcution costs they did away with that long ago. (back in 1990 GM even issued a service bulletin for 89 burbs like mine that added a water cutoff valve to heater core curcuit during A/C max operation because of door/baffle leakage on some models.

----------------- TheSnoMan.com

Not likely.

With undercharge you can get below atmospheric pressure conditions in the system which pulls in (moist) ambient air if there are leaks. The accumulator contains a dessicant packet to absorb any moisture. The dessicant can be saturated if enough moisture is introduced, but that's quite a lot.

Freezing doesn't usually cause ice-expansion damage, if that's what you're worried about, since the ice is typically building up from sublimated water vapor, not liquid water. This is how your household "frost free" refrigerator-freezer works, building up frost on the evaporator which must be defrosted with an automatic heating cycle once or twice a day.

Never happen, the low pressure cutout switch would kick in long before you even came close to negative pressure. It could MAYBE happen in theory if you had a very very low charge and a bypassed low pressure switch but even then the expansion orifice would limit the pressure differentail and keep it from going very far negative and also pump would sieze soon to because with not refrigerant curculating their would be no lube for compressor (this is one reason for low pressure cutout switch)

----------------- TheSnoMan.com

Just got the car back, turns out the initial evaporator leakage damaged the compressor and it could no longer maintain a low-enough pressure to cool on hot/humid days. At about 75-80 degrees ambient, it could only reach 60 psi at the low end, when it is supposed to get down to about 20 psi. A pressure test was performed before repairs and it showed no leakage, refrigerant was at top levels. Verified a vacuum test with 0 leakage for 7 minutes after replacing the compressor. Current air output at any fan speed is 32 degrees and compressor now cycles, which it hadn't done for years before. Hopefully it is done for a long time, and I appreciate the assistance, as well as the suggestion for the bypass to the heater core - I'll look into that for my car. Joe

One would hope so, but the OP said that was faulty.

A leak means you have no pressure sooner or later with the system off. If it is turned on and runs (faulty low-pressure switch), it will certainly have negative pressure (vs ambient) on the suction side, and a leak in that half will pull in air and moisture. Even without running, a leaky system admits air and moisture slowly after the refrigerant is gone. Consider that a system that fails due to a refrigerant leak will often go for months or years before being repaired, so the dessicant will be saturated, just due to amibent temperature and barometric cycling.

A/C technicians often have a superstition that their vacuum pump removes moisture from a contaminated system, including regenerating the dessicant. Not true. You should replace the dessicant (which means the whole accumulator on a TJ) if there's any chance it was open to the air, leaky for a long time, or otherwise compromised.

If you want to regenerate dessicant, you have to bake it. Room temperature vacuum is not enough.

Bake it? Done this? Reliable?

Thanks.

Earle

Low pressure switch is fine, accumulator was replaced again under warranty along with the compressor to avoid the issue you mentioned.

Standard procedure for silica gel or molecular sieve dessicants.

Usually it is for about 8 to 16 hours at 250 degrees to reactivate or dry it out if it is "wet"

----------------- TheSnoMan.com

And note that the stuff will be covered in PAG or POE lubricant, which will present a barrier to outgassing the water.

Yeah brilliant idea. Trying to save yourself 20 or so bucks by baking your old accumulator... Next lets save money on PAG by running motor oil.

I did not say to do it instead of replacing it (I would replace it because it acts as a filter too) I was just saying how to are supposed to reactivate it if you want too. Also, at 250 degrees, the oil would not provide any barrier of concern to steam/water vapor wanting to escape.

----------------- TheSnoMan.com

Not necessarily. Lots of things hold on to water at that temperature by virtue of hydration energy. This is one reason you need a dessicant in the system to start with. Water is tenacious and wonderfully hard to get out of things. The "universal solvent" would rather stay dissolved.

The time or place may come where you have no option.

Please tell me where you can get an accumulator with installation for $20.