By Anne Fonda
A thermostatic expansion valve (TXV) is a small HVAC part that plays a big role in air conditioning systems. This valve regulates the flow of refrigerant entering the evaporator during the refrigeration cycle. A split-system air conditioning system will have one TXV, but a heat pump system may have two - one each for the cooling and heating cycles.
The TXV valve is located near the indoor evaporator coil (“A” coil). There is a sensing bulb connected to the gas line leaving the evaporator. It creates a feedback loop to increase or decrease the mass flow through the TXV to regulate superheat.
This protects the compressor from flooding or overheating. The sensing bulb relies on contact with the gas line leaving the evaporator to accurately sense the temperature of the refrigerant leaving the evaporator and adjust accordingly.
The sensing bulb is connected to the TXV by a capillary tube so it can create a force balance with the other inputs to the TXV. This helps the evaporator operate most efficiently to cool your home.
An electronic expansion valve (EEV) is a more sophisticated, industry-leading, and technically superior refrigerant metering device. It provides more precise refrigerant flow to the evaporator. EEVs control the flow of refrigerant in response to signals from an electronic controller which electronically opens and closes a needle valve.
American Standard cooling systems use an electronic expansion valve rather than thermostatic expansion valves because the technology is best in class.
Troubleshooting and maintenance of the TXV or EEV should only be done by a trained HVAC technician. During annual air conditioner maintenance, they will inspect the valve, associated components, and the rest of your cooling system.
They will clean parts as needed, check for refrigerant leaks, and more, to help ensure your HVAC system operates at peak performance.
If you properly maintain your air conditioner or heat pump, the TXV or EEV system can last for the life of the AC unit or heat pump. If your AC is blowing hot air, you have fluctuating temperatures, or a frozen evaporator coil, a failing thermal expansion valve could be to blame. Call in an HVAC professional to find the problem.
Whether you need AC repair, HVAC maintenance, or HVAC system replacement, work with the HVAC experts you can count on. Contact your American Standard local HVAC dealer today for all your HVAC needs.
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Kimberly Sexton, Senior Systems Engineer
Refrigerant is the lifeblood of an air conditioner or heat pump, responsible for absorbing, carrying, and releasing heat to achieve and maintain your desired temperature.
Also known as the evaporator coil, the indoor coil provides a place for heat to be absorbed and works with the outdoor coil to complete the heat exchange cycle.
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