Hello group..I have a 1987 300SDL, with 242,000 miles on it..The car is in great condition overall and last week we had to have a new turbo put on. Our mechanic did some other stuff and I asked him to check the performance of the converted AC.(134A) which had not had any attention since we owned it.(2+ years) He indicated it was about a pound low. I tried it for the first time yesterday and the compressor appears to be cycling rapidly causing the car to surge terribly..In the past the AC would cause the car to drag when we would first take off, but just that one time but now it seems like it cuts out every few seconds..I am wanting to see if there are things I can check before taking it back out to him as it is hard for me to get to his shop during the week..I read someplace that these cars have to have the pressure switches replaced when converted? BTW the system worked great last summer, been totally happy with the performance of the conversion..But this surging is making me crazy..I quit using the AC..Any ideas? Is this system controlled by a computer?
Thanks so much...John Winn Austin Texas

I'd take it back to the mechanic who last worked on it. If you don't trust him, take to an AC shop - fast! Good luck.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

John,

I'm no expert, but a friend of mine who is says rapid compressor cycling is usually low pressure. You may have a leak starting. Like the others have said, take it an AC person you trust to track it down.

Chuck

My 87 300D cycles quite a bit, but I don't feel it, no drag to speak of.

Be aware that many places still want to overcharge converted systems to "give them more capacity" when in fact you need 85% of the R12 charge, or it won't cool very well.

Constant cycling is usually an indication of low charge, so you may have a leak. Most likely spot is the expansion valve, hard to see on the SDL but easy on the W124.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks guys,
I understand a leak would cause a low charge situation, but the system was working good before, and had never been serviced during my ownership so I would think that a leak would have shown up before..He told me he added about a pound, and then this started..That was why I was wondering if possibly that one of the switches could be acting up...I would find it hard to believe it would all of a sudden have a leak after he added, but I guess its' possible..It does seem to be cooling okay even with the compressor going on and off....
John

John:

If it is overcharged, there is also a high pressure switch that cuts the compressor off. Have it checked again by an AC shop that knows MBs.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

John,

I had a similar problem last year on my '87D. I had the system checked and the pressures were OK. Sometimes it would cycle the way you describe, other times it would quit cooling. Replacing the climate control pushbutton module cured the problem.

ewstan