ac engs -- Servicing HVAC Expansion Valves -- 05-02-16

Servicing & Maintaining Thermal Expansion Valves

What is a Thermal Expansion Valve?

Controlling the flow-rate of refrigerant into the evaporator coil is the sole function of thermal expansion valves, also known as TXV’s (Thermal eXpansion Valve) or as EEV’s (Electronic Expansion Valve) if they are electronic. Both types of valve perform the same function within the HVAC system but through two different, yet similar, ways.

Thermal Expansion Valves

The majority of thermal expansion valves are the non-electric type. These valves use a ‘bulb’ – a small hollow metal body similar in size and shape to a CO2 cartridge, and filled with a similar gas as that in the system – to sense the temperature on the exit-side of the evaporator coil in order to precisely meter the amount of gas flowing into the evaporator coil. These valves are very efficient at their function and are the appropriate choice for most residential applications. The only things that would necessitate an EEV is on higher seer-rated equipment with a lot of variable speed processes.

Electronic Expansion Valves

The newest thermal expansion valves available are electronic. These valves offer a much higher accuracy of refrigerant flow regulation by using several variables to meter out refrigerant into the evaporator coil. On modern, high seer rated equipment with processes that require variable speeds on the blower, is when this valve type becomes essential for a smooth and efficient operating system.

Internal vs. Externally Equalized Valves

In addition to electronic and analog valve types there are two subsets of those: internally and externally equalized. These valve types differ only in how the effect of the evaporator pressure affects positioning of the needle or pin inside the valve. Externally-equalized valves will also compensate for pressure loss within the evaporator coil that can occur through normal operation.

Service and Maintenance of TXVs and EEVs

Generally speaking your TXV or EEV will not require regular servicing or maintenance. However they can experience some malfunctions if they, or parts of your HVAC system, weren’t installed properly. Improper temperature readings by the valve will also affect the way your system operates. If you think that your TEV or TXV could be malfunctioning, our trained and professional technicians at Air Conditioning Engineers would love to assist you. Give us a call today to discuss thermostatic expansion valves, or any other questions you have about your HVAC system, and schedule a home appointment!