afalcfan,
The system is simple.
1) Evap motor Fan Speed Switch on Right turns on the ac system in a 'ready state'.
2) Thermostat Switch on the Left changes the state.
Fully CCW (to the left) is off, or warm,
Fully CW (to right) is max cold.
The thermostat has a sensor (a metal tube filled with refrigerant gas; the tube is between a bellow in the thermostat and its end is crimped; hence a sealed unit).
The sensor goes inside the evaporator. When the evaporator is warm and the thermostat is set to a particular degree of 'cold' then power flows through the
thermostat to the compressor. As the evaporator gets too cold at that set point it turns off the compressor. The refrigerant gas inside the sensor tube expands
and contracts and tuns on and off the compressor.
Read:
The AC Temperature Switch - An example in detail with a typical 911 Porsche
here:
troubleshoot-the-ac-system/