I am driving one of my 123's this winter that I never used in the winter before. I went out at 4:30 this morning to warm it up a little before leaving for work. I plugged in the block heater at 4:30, started the car at about 6:00, no problems. I cranked the heat up all the way, pushed the defrost button, but nothing happened. Went back inside to put some clothes on instead of just a bathrobe. When I went back out, the defroster was running just fine and even eeking out a little warm air. The car got nice and hot on the way to work. Is the A/C - Heater control smart enough to not turn on when everything is still bitter cold or am I heading for trouble.
Thanks Much.

My experience has been that, yes, it is smart enough not to turn the blower on until there is heat to blow. I have had both the older ACC units--with the vertical push buttons--and the newer ones, with the horizontal push buttons. Neither would start blowing until there was a least a semblance of heat generated by the engine.

Joe B.

And thank you. Guess this means the one on the other 300 isn't right, it turns on immediately. It also isn't a real warm car, probably needs monovalve work. Have to wait till spring for that :-)

I believe on both styles of heater controls there is a temperature sensor that prohibits the fan from operating until the temperature reaches a certain level. On my 85, if I start it up and drive down the street, it permits heat to begin within the same 100yds about a half mile down the street time after time.
The defrost button overules this temperature sensor.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13