A couple of different things can be wrong. I have seen where the systems loose vacuum and do strange things. There is a vacuum line that is under the battery that loves to break.
Also the heat valve on a 190 is an on/off vacuum valve.
The other thing is a loss of freon.
You need a good tech to give you honest advice.
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
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