The early 124 cars to 1990 had a smaller compressor that just isn't up to the task. The later cars have a larger compressor and the mounting is different which keeps one from using the later compressor.

Before worrying about the conversion be sure there are no other problems. I would worry about the recirc door being open.

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