How AC expansion valve system works
Auto AC Expansion Valve System Operation
Many car makers now use automotive AC expansion valves instead of the less efficient orifice tubes in their AC systems. An expansion valve is simply a refrigerant metering device to control the rate of flow of refrigerant into the evaporator located in your dash. In the illustration below, you’ll see that low-pressure refrigerant gas flows out of the evaporator coil and through the expansion valve. As it flows, the refrigerant’s temperature is detected by the rod running through the port. The rod is attached to the diaphragm at the end of the valve. Based on the difference in temperature between a gas in the outer portion of the diaphragm and the temperature cooled by the rod, the diaphragm moves a center metering rod in or out of the high-pressure port to meter the refrigerant into the evaporator. It’s really that simple.
Refrigerant flow through the system
When the AC compressor engages, it sucks low-pressure refrigerant gas from the evaporator. The compressor then compresses the gas into a high-pressure gas and forces it into the condenser. During the compression cycle, the gas rises in temperature. Airflow across the condenser cools the high-pressure gas, causing it to condense into a high-pressure liquid.
The high-pressure liquid refrigerant passes through a receiver and is dried to remove any moisture. It then flows to the metering port on the expansion valve. Once the high-pressure liquid passes through the metering port, the liquid pressure drops and the liquid begins to fill the evaporator. Airflow across the evaporator causes the liquid refrigerant to boil and become a gas again. The heat from the cabin air is what boils the refrigerant causing it to change state from a liquid into a gas.
How AC expansion valves work
What goes wrong with an expansion valve?
Expansion valves can fail in three ways:
- The metering rod gets clogged with AC sealant.
- The metering rod binds in the port
- The expansion valve diaphragm develops a leak, preventing the metering rod from moving.
Clogged expansion valve
©, 2018 Rick Muscoplat
Posted on by Rick Muscoplat