Does the A/C actually work in the car? If it does and the return line to the compressor is getting cold, the monovalve is a very likely culprit.

The sensor in the dome light is what sets the mode of the HVAC system to control the vent temperature. Think of it like the sensor for the thermostat on a central AC unit. There is a suction fan or venturi somewhere in the dash that has a tube that runs up to the backside of that sensor and gets air pulled across it all the time. Depending on on where you have the temperature wheel set, various functions of the HVAC system change in response to whether the cabin temp is above or below where you have the wheel set. If you delete or block that sensor, don't expect your HVAC to work.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]