My recently acquired '84 300CD has a strange issue with the ACC. Upon start-up the ACC will do nothing unless you first press the defrost button then switch over to other modes which seem to work OK, including ECON which is the mode I use most this time of year, for heat.

I have a spare temp controller (the metal can under the dash, not the pushbutton unit in the center) that I know is good so I was going to try to change that out but if anyone has any tips on what could be causing this can they please post it? I don't think it is the pushbutton unit since it seems to be related to starting the unit from power-up each time. Once it is working it seems to function more or less as it should until the next time you shut the car down, then you need to push DEF again to get any of the other settings to work.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz