2002 Dodge Durango A/C

The A/C switch is possibly a reference to a pressure switch usually located on the receiver/drier bottle, its function could be two things, a low pressure and a high pressure sensor, usually incorporated into one sensor with 4 electrical contacts. So if there is no pressure, then the clutch cannot be commanded on, and if is too high or the evaporator core reaches a set temperature, it disengages the compressor. If the system has oil in it and freon will not go in, check for proper charging, are you filling from cans or a 30lb canister? As soon as that switch sees pressure it should allow the compressor to engage and then fill with the proper amount of refrigerant.