Correct me if i am wrong. Do you mean that switch which is mounted on the top of the AC bottle through which we see the gas flowing once the compressor is working.

If this is the switch you are talking about then it is having two wires on it. So witout starting the engine and with the key in the agnatition switch with the dash lights one, both the wires should have 12 v current in them, or i should start the engine and the should check the voltage in both of the wires on this switch

Thanking you