If I charge it with 152 and then evacuate again will I contaminate somthing?

Well, if you evac it into a machine with 134A, yes. You will destroy their recovered refrigerant...but seeing as how 152A comes in air duster cans, you can just release it into the atmosphere and it is no big deal. :)

Initially I had 134A in that 300E as it was all I had on the shelf. It leaked out, so that is when I tried the 152A. Cheaper and worked better. R12 would be better, but for $15-30 for a 12oz can versus $2-5 in...it was a no brainer for me. The car cooled very nice for me.

Make sure the condenser and radiator are clean. Need to pluck the rad to pull the condenser far enough back to pull the dual aux fans. It is worth the hassle. Also, the only fan clutch that worked for me on the M103 was the Sachs. With no air flow over the condenser, you will have weak AC always.

To educate myself and to be able to buy R12 I went ahead and got 609 certified. It was easy. I read the booket (about 60 pages) and took the test.

I have decided that putting R152a is not worth the risk. Perhaps the EPA is being over zealous but they feel that it is a safety hazard to run it in a system that runs the R152a through the passenger cabin. Apparently it is flammable under certain conditions.

I figure Ill just run it the way it was designed. From what I have read I think the compressor on these things is supposed to run all the time unless:

1. The AC is switched off
2. The high pressure side is below about 40psi (mine was at 50)
3. The receiver dryer gets over a certain temperature

Plus my pulley does not "retract". It either spins or does not spin so they must have changed compressor designs at some point in the life cycle of the W126.

Anyhow. I charged up my system with my 2 cans of R12 freon and injected some dye in the system. Presto - Cold air.

Now Ill watch for the dye and how fast it leaks out and then Ill repair the leak and evacuate and recharge with a fresh R12 charge by weight.

Nice, glad you have conditioned air again. :)

I believe you are on the right track. If I remember right, they used to have freon with "stop leak" in it. Whether it worked and did not harm the system, I know not. Just a thought. Good luck.

Yours is easier than mine on my '81 300SD. I had a terrible squeak which I thought was the water pump. Turned out to be the compressor. So I cut the belt and now need to replace it. Not to hard; just tedious.

The stop leak freon will kill your compressor. The leak is usually shot compressor seals, anyway. New compressor isn't crazy expensive and you don't have buy a MB factory unit, as they are an OEM manufacturer part. If you see green dye on the back side of the pulley, plan on swapping the compressor before it blows up and sprays metal into the whole system.

The stop leak will also kill the expansion valve if you have any air or moisture contamination in the system. When it goes, plan on converting to 134a, the modern 134a expansion valves have a smaller orifice size than the R12 ones did and they're all that's for sale.

I have used leaking compressors for YEARS on various vehicles. They do not just blow up at random. They seize when the system has very low/no refrigerant as the gas moves the oil. Keep it full and it will keep running.

Even my dumbass R4s on the SD were like this that had no sump. Now I have a Sanden from Klimakit and I will never run a 617 again without a Sanden on it.