A/C leak. Where?
 

Hi. I have 1990 300E 184,000ml
my mechanic recharged ac system with dye to find source of freon leak. system leaked out but he cant find leak anywhere. there are few tiny spots on expansion valve he says they are so tiny that it is impossible to leak all freon out through them in a year. my system leaked out in a month. are there any common sources for freon leak in 300E?
Thank you

Evaporator core?
Larry Bible (lots of A/C knowledge) gave me this suggestion:
Recharge with dye, look at the condensation water. If the dye is there, then the evaporator is leaking.
He told me this after I could not find a leak anywhere in the engine compartment.

pesuazo
 

Thanks for info. Shop people looked into evaporator drain but its obviosly dry so you cant see any dye in it. Ill recharge system again with dye and check water coming out of evaporator drain. I also found changed expansion valve o-ring since there were tiny spots of dye. Also if evaporator leaks freon will it smell inside cabin?
Thank you

Dye usually works, but not always. When dye fails, it is best to put in 2 oz. of R22 and pressurize with nitrogen then use an electronic leak detector. An electronic leak detector is very sensitive R22, that's why it works so well.

Don't even think about replacing evaporator unless YOU ARE CERTAIN that it is the leak source. They are not destined to fail as some people say. Mine has the original evaporator and is blowing 38 degree air.

The expansion valve is a somewhat common leak source. They will leak at the top where the diaphragm meets the block. It is hard to see the dye. I could barely see dye on mine, but there was an oily film around it which is another clue of a leak. Once I took it out and shined the black light on it, it was very obviously a considerable leak source.

Good luck,

Thank you very mych for input. I checked expansion valve and it looked good under back light so I ended up replacing o-rings since ther was spots of dye around piping. Mechanic recharged the system and now there is a bigger problem. First compressor would run for 1 second and would shut down. Mechanic said there is a clog in system since compressor puts out a lot of compression but it doesnt go anywhere so it shuts down. Then he played with his valves and got compressor to work stable. But system blows out around 78 degrees! He says that I have to change hose from dryer to condenser( he claims there is filter in that hose) and to replace expansion valve and possibly evaporator. Now Im totally confused. First recharge of system used to give out around 60 degrees. I only changed front o-rings on expansion valve nothing else. And today I were driving and AC stoped working. I restarted the car AC came back on then once I were near my home it shut down again. I checked sight glass no bubbles there. So now Im totally confused. Any body have any suggestions? Shall I change expansion valve and that hose? Thank you very much.

Victor, it seems that your mechanic is b.s. you.
I mean if he only had to change couple o-rings for the small leaks, why does the system is clogged now?
If I were you I would takje it someehre else or try to troubleshoot myself.
The last thing you want to do, as LarryBible said, is to change your evaporator.
I have not done it for any benz, but I did ot on a Nissan (very difficult).

good luck