Being a entry model 123 chassis I presume it has manual A/C not Climate Control. From the year this would mean a simple "ranco" style evaporator temperature switch. This is the same type switch with gas filled capillary tube into evep that works on old refrigerators/water coolers/Coke machines. Power comes in and is switched to the compressor through this switch which in MBs case is a fixed (non operator adjustable) temp switch. It is located behind the glove box.
Power comes through the blower switch I think and goes from the evap switch through the low pressure switch. Many places for poor circuits.