Expansion Block/Orifice Tube: Description and Operation

A/C VARIABLE ORIFICE TUBE
A Variable Orifice Valve (VOV) is installed in the liquid line between the outlet of the condenser and the inlet of the evaporator. The inlet end of the Variable Orifice Valve has a nylon mesh filter screen, which filters the refrigerant and helps to reduce the potential for blockage of the metering orifices by refrigerant system contaminants. The outlet end of the tube has a nylon mesh diffuser screen. The O-rings on the plastic body of the VOV seal the tube to the inside of the liquid line and prevent refrigerant from bypassing the metering orifices.

The VOV is only serviced as an integral part of the liquid line. The VOV cannot be adjusted or repaired and, if faulty or plugged, the liquid line unit must be replaced.

The VOV meters the flow of liquid refrigerant into the evaporator coil. The VOV contains two orifices which work in parallel. The fixed orifice works along with the variable port to regulate refrigerant expansion in the evaporator in a manner that is suitable for most operating conditions. The high-pressure liquid refrigerant from the condenser expands into a low-pressure liquid/vapor as it passes through the metering orifices and diffuser screen of the VOV

The VOV varies the flow of refrigerant in response to the temperature of the refrigerant exiting the condenser. A thermostatic bimetal coil wrapped around the valve body is affected by the refrigerant temperature changes, which opens or closes the variable port to regulate refrigerant flow. As the refrigerant temperature increases, the variable port is progressively closed. A higher temperature (while idling) produces more restriction. A lower temperature (at road speed) produces less restriction.