A/C leak problems

OK, working on my brothers '97 XJ trying to find an A/C leak. After putting several cans of UV 134 in it we still cannot find the leak. We of course have only looked at everything that is easily visible. The only place left is (horor) under the dash. Has anyone experienced a leak in the evaporator? When fully charged the system goes down in a week enough to trip the low presure switch constantly. How did you find the leak when you have too remove it to see? I hate to take the dash apart, but its the only thing left and the thing we cannot see.

Angus

if its a jeep the evaporator will leak. its not that bad of a job afterall.

Just an idea, but before I´d tear the dash apart on a hunch, I´d find a litte R-22 someplace and add couple of ounces to some 134a (or use dry nitrogen if you have access to it) and do a test with an old flame tester or old style freon tester. If you get some pressure in the system, leave the windows rolled up for a weekend, the inside of the car should be pretty saturated with R-22 and show a green flame. The carpet down by the evaporator, would be a good spot to check, with a flame tester, freon-22 will settle to the floor if undisturbed. R-22 is less ozone depleting than other refrigerants. A couple of onuces of R-22, compaired to how many of 134a? Sometimes common sense has to prevail, over environmental concerns.
If it takes a couple of weeks, it´s a tiny high pressure leak or a small low pressure leak. Even with stain freon, it could be hard to spot.
Another possibility is behind the mag clutch at the shaft.
I do a close visiual, systematically with a flashlight and look for oil stains. When I find a questionable spot, I soap it up. Have found leaks, with a 1mm bubble every few seconds, have to look close.

if you have no oil seapage from any a/c fittings and all the lines ang condensor are dry you probably have a bad eavporator. i dont recommend adding anything else to your system that isnt approed, that can contaminate anyone elses systems that may share the same charging machines that your vehicle can be hooked up to in the future, and can cause costly repairs to the service station's machines.

Yea, we started by looking for traces of oil. Of course in this case his jeep is spotless. My 2000 has had an oil stain on the hood above the compressor clutch since new, but never has needed a recharge? We have gone over the whole system in pitch black with a UV lamp and nothing is showing up. I guess I am looking for support of my logical conclusion that the evaporator is the culprit.

Angus

the jeep is 7 years old. we see newer wj's at work that leak. i would say by now the evap is gone, you can also look in the a/c drain tube for traces of dye, that would confirm the evap is leaking, depending on how much dye was in the system.

Jneary is a Jeep Tech. guess he knows his Jeeps, if he says the evaporator is the probable source, he is probably right. Sometimes assumptions work out.
The time Jnearx spent on Jeeps, I spent on refers and A/C´systems. Been fooled a few times. I rarley wrench, until the options, have been explored.
I´m a troubleshooter, usually the last in a long row of mechanics and tech.´s to look at a machine. I usually expect it to be hard and not the run of the mill problems. I usually assume the worst, look for the unusual.
Right at the expansion valve is a fairly common place for leaks, coldest part of the system, a lot of expanding and contracting.

Yes, I have looked at the drain tube, but nothing found yet. That is one of the reasons we have continued to recharge the system with die. I am hoping to eventualy leak enough UV out to make it more visible. Of course if the leak is in the HVAC box that will be hard to do.

I am a mobile mechanic that does very few A/C jobs. If its obvious Im good, otherwise Im a dope.

Angus

well if you have a leak and cant see it, it must be where you cant see. i bet once you get the evap out you will see tons of oil and dye on the evap coil.have you ever noticed any different smell when running the a/c?

one word of caution, make sure to disconect the temperature control cable from the heater case or while pulling the dash away from the firewall you will bust the lower half of the heater case.

Hi
It took two weeks for the dye to come out of the drain. It was the evap that had to be changed.
Changing it : easy.
Reaching it : ouch!
Six hours all together.

I was looking thru harbor freight and noticed that they have a vacum pump, electric, that can be used to dry out an A/C system, costs $9, add a couple of hoses and a vac gauge.

Hard to get a good vacume, the better the pump, the better the vacume. But any vacume is better than none.
With a pump less than ideal, a vacume and purge system can be used, dry nitrogen is the prefered purge gas. With gases, the container is often the expensive part of procurement. Don´t know if dry nitrogen is available in Quick cans. When purging, very low pressure is used, allowing the dry nitrogen to pick up as much moisture as possible and not move any more oil than necessary.
Moisture is a major problem, but air also contributes, air expands by volume a lot. Drives your high pressures up and displaces liquid freon, and can cause low pressure problems.