W126 1991 560SEL A/C leak - PeachParts Mercedes-Benz Forum

alabbasi · #1 05-23-2011, 10:17 AM

On my 1991 560SEL, I have a very frustrating leak in the a/c system. The car would hold pressure to 75psi on the high side. The rest gets leaked out. I replaced the condenser, low side hose and compressor.

I pulled a vac and it held, then I charged the system and used my sniffer to check for leaks. Nothing showed up at the condenser, lines or compressor, so I stuck it through the vents and up by the gas pedal where the expansion valve is supposed to be. Still no leak detected.

I've recently replaced the compressor and the condenser on this car in an effort to cure this problem.

Any thoughts as to where this leak could be would be gratefully appreciated. It's going to get hot in Texas over the next couple of months.

nulu · #2 05-23-2011, 05:23 PM

Check the evaporator behind dash, put dye in it then check ac drains under car to see if dye traces are present , its very common for evaporator to leak.

duxthe1 · #3 05-24-2011, 11:44 PM

What are your pressures when the system is full? With this scenario I'd be suspicious that the fans aren't up to snuff causing high side pressure spikes. In which case it would only leak during pressure spikes and be very hard to detect. Flourescent dye is essential for finding difficult leaks.

alabbasi · #4 05-24-2011, 11:50 PM

Thanks for responding, I only measure the pressure when I charge the system and at that point I charge to no more then 225psi on the high side. I will check the fans.

Hit Man X · #5 05-25-2011, 02:28 AM

Did you reseal the expansion valve? It is a BIG PITA so most cars never have it done. My SDL slowly leaks from there and my 300SEL used to also.

alabbasi · #6 05-25-2011, 11:14 AM

Eric,

I haven't touched the expansion valve, my buddy David Poole seems to think it would be there and the sniffer may not pick it up because it's covered with some sort of insulation.

It looks like a job for trained limbo dancers.

lorainfurniture · #7 05-25-2011, 11:59 AM

Quote:

Originally Posted by alabbasi

Eric,

I haven't touched the expansion valve, my buddy David Poole seems to think it would be there and the sniffer may not pick it up because it's covered with some sort of insulation.

It looks like a job for trained limbo dancers.

You can peel away the rubber stuff and put your sniffer to it.

It was the biggest pita job I ever did.

graftdesign · #8 05-25-2011, 04:49 PM

I recently discovered one of the nuts on the line from the receiver to the condensor was bad. It literally broke in half when I touched it so it was obviously the source of my leak. This is the line that's right next to the air intake to the right of the radiator.

I didn't notice this until I was swapping out my US headlights for Euros. It's in a hard to see spot otherwise.

Worth a look. I too was stumped about my AC until I saw this.

Hit Man X · #9 05-25-2011, 10:21 PM

The late 126s are a REAL bear due to that extra crash bar/dash support RIGHT in the way. I mean, RIGHT in the way. I just do not trust 20 year old o-rings.

The dealer even diagnosed my 300SEL as 'bad evap core' to the PO before I purchased it... all that was the matter were bad o-rings.

I would agree with David. I have a slow leak on my low side schrader valve so I am going to visit him pretty soon. I do not have time to hunt down a recovery machine plus it is summer so everyone is going to want $$$$$$$ for them.

Not to mention it is silly wasting R12.

hbofinger · #10 05-28-2011, 11:36 AM

I did a writeup on replacing the valve. You can find it at this link:

http://www.funnyyouasked.com/Mercedes/W126/ExpValve/removal_and_replacement_of_expan.htm

The part is not very expensive. It is imporant that you know how to empty and refill the system, which (by your post) I suspect you know. Figure about an afternoon.

Good luck!

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