The heat from air conditioner problem is caused by a stuck/failing heater servo/heater valve. An expensive part. Try to buy it used. Contact Sun Valley Mercedes Dismantlers and ask for Marc. He is very knowledgable and may have a valve that fits your car with less age or mileage than yours. Labor to put it in is nominal and Sun Valley warrantees parts for I think a year.
I have vacuum problem also, but have not been willing to incur the cost to try to fix it.
Tell Marc Jim from Chicago suggested you contact him.