An AC sensor tracks system health to protect the A/C compressor. The pressure sensor measures refrigerant pressure in the lines. If pressure drops due to a leak, the sensor sends a signal to the engine computer. The computer then disables the compressor clutch to prevent the pump from running dry.
Evaporator temperature sensors prevent the cooling core from freezing. If the evaporator gets too cold, moisture from the cabin air will freeze on the fins. This blocks airflow, causing the vents to blow warm. The sensor tells the system to cycle the compressor off before this ice forms.
Modern climate control systems also use cabin temperature and solar load sensors. These sensors track humidity and sunlight strength. This lets the A/C computer adjust fan speeds and vent mixing flaps automatically.