Questions to AC Experts.
 

I have a very elusive AC leak. Not a big leak mind you but still a leak. I loose about 3 Oz. of R134 per month. That about 10% of the total capacity of the system. I've added UV dye, and still can't find the leak.

So here is my question. Using a UV Light, I checked the Condensate water dripping from the evaporator onto the driveway for traces of UV dye. No trace of UV dye found, the condensate was clear. Does that eliminate the evaporator as being a potential cause?

Don't know where else to look.

Thanks

I am neither an expert nor a professional mechanic. I've have replaced the evaporators on three 124 MBs recently and I'd have to say the answer to your question is mostly likely no. If you can not find the leak it probably is the evaporator.:(

See this thread.http://www.peachparts.com/shopforum/showthread.php?t=152840&highlight=evaporator

Edited:
Below are a couple of photos of car with dash off, one with evap box and crash bar still in car and the other with them out.



http://forums.rennlist.com/upload/evap_te_001.jpg

http://forums.rennlist.com/upload/evap_te_002.jpg

Wow. That's not the answer I was hoping to hear. Those pictures are totally depressing.

In the link that you referred me to, (where you say that the leak was not big enough to notice any UV dye in the condensate). How big of a leak was it? How often did you need to add R134 and how much were you adding?

My leak is about 3-4 Oz/ Month. Was yours more or less?

In my opinion it rarely is the interior evaporator, its always seal rings and stuff like that, or the evaporator in the front because its exposed to road salt grime and rocks .. my dad has trucks that passed a million miles and we never changed any evaporators inside the cab.. problems are always outside where the components really take a beating.

Some models and years eat evap cores.

I believe the problem was due to the use of dissimilar metals (aluminum and copper) and the differential expansion/contraction of these metals as they are heated/cooled over time leading to failure of the joining of the metals causing a leak. <- I could be wrong though :)

I can not say for sure, I bought the car in Dec of last year. I filled the system with about 2.1 lbs. two months ago and it progressively lost it’s ability to get real cold. The other big problem was air barely blew out the center vent, it blew thru defrost vent, that meant the vacuum element was leaking. There are 6 vacuum elements that control air distribution, they don’t last forever.

Look at the lower right side of the photos I posted in the thread in the link I referred you to, post #1. You can see a little greenish oily tint on the bottom of the evaporator and in the case. It never leaked enough for any oil or dye to come out the bottom of the evaporator core. Also you can smell the oil on the evaporator, it’s quite nasty smelling. Sometimes people with bad evap leaks will complain of the interior of car smelling from ventilation system.

To make the A/C function like it did when car was new I replaced stuff I mentioned in the thread I linked to.

Four of the cars I work on are 124's and all of them have new evaporators. Actually, one of them, a 1992 had a new evaporator 8 years ago, it was done by an independent for prior owner right before I bought the car. My expectation is sooner or later a 124 is going to need either a vacuum element replaced or the evaporator.

If you have to take it apart for an element you might as well do the evap too. That’s what happened on the one in the photos. It turned out the evaporator was leaking, which is what I suspected, and I had 3 vacuum element that also leaked.

A/C evaporator failure rate in MB CARS thru the 1990's has been very high at somewhere around 8-10%!..IN the summer we replace at least 200-300 of them.

Seems like the Germans are just now figuring out their DESIGN problems!

The only MB that has very low evaporator problems during that time was the ML...that system was designed by DENSO in the USA...not by Behr OR Valeo in Europe!