MB DOC. My understanding is that baffles which allow the heat through are controlled by vacuum. The scenario is that my mechanic took the heater control unit out of the dash to see if we could get some of the buttons n the panel working. The only thing working was the defroster button for heat and the high blower for a/c. After he put it back together, I only have cold air blowing out of the defroster vents and, at the beginning of turning on the blower, out of some of the dash vents. During the process, we discovered that the top of the radiator was not getting hot and two of the water lines on the "heating control unit" (if this is the correct name) mounted on the passenger side firewall in the engine compartment were not getting hot. We replaced the water pump and thermostat and now we are back at no heat and only cold air blowing out of the defroster vents. Our current thought is vacuum, but I am open to any assistance.

Thanks. SMW