A/C Leak Diagnosis Help

[R1990]

Hello all. The car is a 1990 300SL (R129) and I have a pretty big A/C leak. It takes about 4 days for 1 can of refrigerant to fully discharge. I know all leaks are different, but would this kind lead me to believe that its mechanical, i.e. from the compressor and not from any seals? Thanks in advance.

[a2aa]

You need to diagnose the source of the leak. Attach gauges and read the pressures. Charge with dye then look for the leak. And hope that it's not the evaporator.

UV dye and a black light is the most common method. Once charged with UV dye, run it enough to make condensation drain water underneath the car and check the water with your black light for traces of dye. If it is present the problem is most likely the evaporator. Look everywhere, particularly at the joints, condensor and compressor shaft seal.

With such a substantial leak this method should find the leak.

Good luck,

[Kestas]

UV dye is the standard for finding a/c leaks. But if the leak is big enough and the system still has enough charge, you might use soapy water to look for leaks.

[duxthe1]

First thing you should do is test the auxilliary fan. Bridge the high temp switch and the fan should run. If it doesn't then your high side pressures will be way too high a lot of the time. This excessive pressure strains almost every component in the system. U/V dye should find the leak. Make sure the fan runs to prevent a re-occurance.

[R1990]

Well guys, I loaded the system with oil and a can of refrigerant while I searched for a UV dye. The next day, I found puddles of dark oil under the middle of the car. At first, I thought I had either a motor oil leak or a tranny leak. Upon closer inspection of the oil in the driveway, it seemed too thin and too dark to be either motor or tranny oil. My guess is that the evaporator is shot and leaky and the oil is actually coming from a leak at the evap. I think that the oil leaked out and mixed with all the gunk that's under the car hence giving it a very dark appearance. Do you guys think that my assumption is accurate. If so, I am planning on a complete system overhaul with a new evap, drier, compressor, expansion valve, and seals. My compressor was very loud and thats what prompted me to add oil. Now the engine is quiet but the leak is extensive.

No, I don't think that this is a valid diagnosis. It would be a VERY unusual circumstance for drain water to be oilly.

Did you put in UV dye and use a black light as I suggested? If you put in UV dye and the evaporator is indeed the leak source then you should be able to see the dye in that oilly puddle.

Good luck,