Sounds like the switch is working as designed. It is a low pressure switch, designed to prevent the compressor from turning on if there is low/no refrigerant in the system.

There is another version of the switch, designed for R134A applications that is both a low pressure and high pressure cut-out. This prevents overpressuring the system from the interently higher system pressure R134A refrigerant.

When you get gauges on it, I'll bet it shows an empty system.

__________________
Bob
'82 300D Petrol B-G Metallic