Climate Control 1985 Mercedes 300D

[3eagles]

I've had ongoing problems with my climate control for a long time. I've replaced the auxiliary water pump, rebuilt the mono valve (run with it connected of disconnected make no difference) Replaced the soft temperature sensor hose and the sensor and still not correct. Usually I start out warm but the systems quits and starts blowing cold. Often if I stop and restart the engine the heat will come back. Seems worse after acceleration.
Now it for this winter it has a new problem. It is blowing warm air out of the passenger side only. It's working on the side vent, defroster and passenger side center vent. The drivers side blows cold. I figure its a vacuum actuated valve but I've tried manually moving the levers and nothing changes. Is it possible that the AC is trying to run at the same time as the heat? I cant afford to send it off the the dealer for repairs. Any help will be greatly appreciated. Chuck, cold in NH