[1983DieselW123300D]

had my 1983 300D air conditioning compressor go out. The condenser and all lines had to be replaced because of junk in the lines and the old one "shattered" part into the lines The old system worked good right up to when the compressor froze up. New one put in all sorts of issues, the shop that did the work, a independent Mercedes garage wound up having to send the car to the local M/B dealership 3 times to replace bad compressors and once I know because it was said the auth. dealer messed up After being n the shop for 4 months, the repair lasted for about a month. Took it back and Oh no! a new issue, not enough PSI to get the A/C going or keep it going. It was determined a leak in a back door had to be traced and fix. Now I have to admit the Vacuum system works better than ever but this time when I picked it up the A/C did't even work long enough to get me home, I noticed after about ten miles the compressor had shut off, extra fan off and warm air. My question is why and how and what does the vacuum system do to keep the a/c working. The a/c worked amazingly well for about 20 min then just stopped. The shop suggest a $3,000. replacement of the vacuum system might be needed to fix the issue even though it worked fine with my old a/c and like I said a major lead was fixed SO other than moving the vents around for air to defrost or heat etc., what does the a/c have to do with the vacuum system? What else could my issue be? I know you need vacuum to shut off, make the kill switch work. worked great before and now... Really need help... out of money to do any more Thanks John:crying

 

[rocky raccoon]

You are correct

All the vacuum system does is direct air flow. With no vacuum, the a/c will default to the dashboard vents.

Check your monovalve. If the diaphragm is ruptured, the heating system goes to full heat and will overwhelm the air conditioner resulting in warm air coming through the vents.

 

[1983DieselW123300D]

Thank you Rocky Raccoon, kind of what I was thinking... Frank's European was trying to sell me on a possibility of a $3,000. dash repair.
sorry I'm not very mechanical but ,. I know now Ive been put in the dumb pile for a while now at this shop.
While having the lock system work, it wasn't why I brought the car in... thanks

 

[DeliveryValve]

Where are you located? Perhaps some other local to you members can recommend a reputable shop. That Frank's is taking you for a ride.
As rocky stated, it has nothing to do with A/C operations except for directing air flow.

Couple basic things you can do is check to see if the compressor is spinning when the A/C is on. Also see if your front Auxillary Fan is on. If any of these are not running, you can be low on freon. If they are running, then you may have issues with the Mono valve as stated earlier, bad compressor, bad expansion valve, bad evaporator temperature sensor or even low freon again.
Speaking to freon, what did they use to recharge your system, R12 or R134a?

 

[1983DieselW123300D]

Thank you for the reply and according to my service advisors and paper work and cost.... all those items were replaced except the I don't see the monovalve being on the six pages.
The freon has been checked every time and no leaks and show full. It's funny because I drove it a couple of times now and it seems to stop working after about 10 to 20 miles... or about 20 minutes.
Short drives the a/c works and when I stop, say go to the gym and come out, the a/c will work. Once the a/c stops on the road, it takes a long time sitting before the a/c will start up again.
The good news I just got a e-mail from the owner of the shop, and he said they would get to the bottom of the issue and fix it no charge. So a week from now I have the appointment, and yes it's going on to six months now.
Thank you, John