Car is 1987 w124 300D. USV

I live in a tropical country and the heater components have been taken out. Is it normal that my compressor does not turn off even at the lowest setting? Or is there something wrong with the AC control module? If I don't have the heater components, will the AC control module not be able to turn off the compressor / will it not be able to regulate and set the temperature using the (blue-white-red) Dial?

The previous owner retrofitted a rotary thermostat in place of the evaporator thermostat. I tried to put it back to original by installing the correct thermostat. AC Compressor engages but it seems not to be able to regulate. It is very cold. Temporarily, I placed back the rotary thermostat to regulate the temperature but it is somehow "spotty". It doesn't regulate Linearly. Most of the setting in the dial is either off or too cold. There's a (small) sweet spot where I can get a good enough comfortable temperature.

The buttons on the AC module still work and the (blue-white-red) Dial still regulates the speed of the blower.

sample of rotary thermostat