I just purchased a 1987 300td. The AC has been repaired and blows cold and strong out of the side vents but is not blowing strong out of the center vent. Also when I put the heat on Max. it still blows cold. Any help would be greatly appreciated.
Thanks

Check for vacuum leaks in the circuit that involves the recirc door, defrost and center vent. The center vent defaults closed and the defrost open with lack of vacuum.

As to the heater look at the electrical control of the water valve. I might worry about someone plugging the lines or wiring the thing on constantly. The heat is off with the valve turned on, it also defaults to hot, which is the normal fault and is often bypassed one way or other to get AC.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician