[Mrmerlin]

that part is called a freeze switch it is used to shut off power to the AC compressor when the evaporator gets to freezing temperature,
this will preven the evaporator from freezing up, it is adjustable via a small phillips screw next to the male elex connector pin.
NOTE you only need to turn it 1/4 turn or less .
You can test it with a glass of ice water,
remove screw holding it to the duct then pull it straight out,
There is a brass tube filled with oil that goes into the fins dip in water and listen for a click this tells you it functioning,
make sure to measure the water temp so you know what the open/close temp is. you must also fit the cowl cover so engine heat will have less of effect on its operation