I just picked up a 1979 300D with a non-functioning A/C. I’ve read about converting from the OEM compressor to an aftermarket compressor. I was thinking about doing something similar, although I would like to go with a more economical Ford or GM standard compressor and drier (and other parts, if necessary).

Although I am not an A/C expert, it looks to me like the 300 D A/C system controls are vacuum operated. [There is a unit next to the compressor that has several vacuum lines running to it and an electrical connection running from it to the clutch.] As most of the vacuum lines are shot on this car, I'd kind of like to convert it to electrical operation/control.

Any thoughts on where to start? Anyone done this before?

 

you have plenty of space for conversion.

the vacuum operates the flaps. replacing it with electrical means using a stepper motor instead of vacuum element.

start stripping out the whole heater box. it takes 4 hours for a beginner with reasonable tools. study, check, and decide.

 

Seems to me that, if I wanted to convert to a different "brand" of A/C, then I could get most of the under-dash equipment from a junk yard. Do you have any suggestions on a make/model of vehicle whose equipment can be fitted more easily? Thanks for the info.

 

for the compressor, it's not a problem. you can fit any brand for as long as the pulley fits the belt. the bracket can be fabricated easily.

the inside, just leave it as it was. leave the flaps on certain position that fits you, except for the blend flap where heating and cool air can be selected by using control cable.