There sure would never be anywhere to hang a unit under the dash on an SL.
Just because the face of the console looks like A/C controls doesn't mean it was factory installed. it is an important question to ask your tech. If the car has Climate control it undoubtably was a factory install. If it was manual A/C then the fact and most all aftermarket used the same console controls. The problem has to do with how they installed the evaporator.
Bosch Master, ASE Master, L1
33 years MB technician