Throttle Valves
Throttle Valve is a choking device to regulate flow of a liquid, for example, in a pipeline, to an engine or turbine, from a pump or compressor. Also known as throttle.This device mounted with the A/C Evaporator as a way to regulate the temperature of the evaporator without cycling the compressor on and off.
Function
The throttle valve acted as a sort of pressure regulator on the evaporator. As the A/C Compressor creates a suction on the low side of the evaporator, the temperature can be controlled by regulating (throttling) the pressure in the evaporator. To low a pressure will cause the temperature to drop and can cause the evaporator to freeze, while too high a pressure will cause the refrigerant to cycle poorly and cause the evaporator to warm up, decreasing the effectiveness of the air conditioning.
Failure
Over time, the throttle valve often becomes clogged or fails internally, restricting refrigerant flow, sometimes completely. This often leads to a situation in which the high pressure side sees excessively high pressures, while the low pressure side sees excessively low pressure. This is in addition to little or no cooling occurring at the evaporator. Owners have noted that they can feel one pipe on the evaporator almost (or fully) frozen, while the rest of it is of ambient temperature.