Pilot-operated absolute valves help prevent evaporators in automobile air conditioning units from freezing. General Motors developed POA valves in the 1960s.
A POA valve is a type of suction pressure-regulated valve used to maintain a minimum temperature in air conditioning units by controlling the amount of suction used. It does this by using a sealed pressure element that is able to maintain a consistent level of pressure regardless of the altitude of the vehicle.
Located at the outlet of an air conditioning outlet made for an automobile, a POA valve controls the flow of refrigerant in the AC unit and thereby regulates the amount of compressor suction applied to the evaporator. This prevents the evaporator from freezing.
Newer cars use a thermostat instead of a POA valve. In newer models, thermostats cycle the compressor on and off to prevent freezing. This is unlike older models in which the compressor runs continuously.
