I have a 88 560SEL. I converted to 134 about two weeks ago. The conversion was done by a guy that knows his stuff I believe. He put in the Ester oil to make sure the different oils within the system mix decently. Now, though, the compressor is making a "grinding" noise that it never did before when it still had r12. It didn't do it when he converted it but I think it has gradually gotten louder and louder since then. It starts as soon as I push the a/c button and stops as soon as the button is turned off. It still blows really cold but the sound worries me. I haven't talked to the guy that converted it yet. Thanks.

Why did he convert it to R-134? He can buy R-12 for $15.00 per pound now, so cost of fluid is not the issue.

There are numerous threads that point out the disadvantages of switching to R-134. One of them is the significantly higher system pressures which shorten the life of the compressor. Your's might be reaching the end of it's life, unfortunately.

One of these days, I'm going to REVERSE CONVERT back to R-12.

Well if he did not flush the system to completely remove the mineral oil, he does not know what he is doing. The mineral oil for the R12 and the ester oil for the R134 do not mix and cause neither to stay in suspension. This causes a lack of lubrication to the compressor. He did the conversion wrong.
If he is a licensed (609) AC service mechanic then have him do the job right.
But by what you have told us, assuming he did not flush all hoses and replace the reciever dryer, then I would not trust him.
If the system was not flushed, it MUST be flushed now to remove the 2 oils in the system. All hoses disconnected and flushed. The reciever/dryer replaced ( anytime the system is opened its a good idea) and the expansion valve replaced if not R134 compatable.

But why did you convert????? If the system had failed then OK but if it was just low then R12 would have been better.

We need more info.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

The reason the a/c was worked on was that it had started to blow warm. What we found was that the hose going from the compressor to the condensor was bad. The oil inside the system was leaking from it. And that was the only leak coming from the entire system. I have had other cars converted in the past and never had any problems, so I really didn't give it another thought. I will admit that he recommended flushing the entire system but, once again, in the past that wasn't done on other cars I had and the compressor worked fine in all cases. The other cars were an 89 Mustang and an 89 Ramcharger. I owned both for at least two years after they had been converted with no problems. He told me there was a chance the compressor might act up but in the past he had seen it go both ways, some are fine and others can't take the conversion.