Home AC Expansion Valve

Learn about your central AC unit expansion valve, how it works, and the signs of trouble.

First, there are two kinds of AC unit expansion valves: the older thermostatic expansion valve (TXV) and the newer electronic expansion valve. Whichever type your AC has, it’s a small internal component with a big job.

The AC expansion valve is located near the indoor evaporator coil. The evaporator coil is located inside your air handler, or in a coil case next to your furnace. The valve is located right where the refrigerant line enters the evaporator coil, or “A” coil. 

The AC expansion valve controls the flow and pressure of refrigerant to the evaporator coil during the refrigeration cycle. The liquid refrigerant entering the expansion valve is very warm. As it makes its way through the valve, the refrigerant cools before it enters the evaporator coil.

The TXV expansion valve has a sensing bulb that detects the temperature of the refrigerant and increases or decreases pressure and flow accordingly. It’s a mechanical operation. 

An electronic expansion valve (EEV), on the other hand, is a more sophisticated, industry-leading, and technically superior refrigerant metering device. EEVs have an electronic controller that electronically opens and closes a needle valve. This offers precise control of refrigerant flow. All Trane cooling systems use an electronic expansion valve.

When you maintain your system, the average expansion valve should last about 15 years, or for the life of your AC unit. However, eventually, the part may wear out or fail. Here are some indications that you might have a bad AC expansion valve.

If your AC won’t turn off, it could be a problem with the expansion valve, among other things. Your air conditioning system has temperature sensors that are supposed to turn the system off automatically once it reaches a set temperature. An exception to this shutting off would be a variable speed system, which runs longer at lower speeds to maintain the temperature and reduce energy consumption. 

A bad expansion valve can also cause a frozen evaporator coil. The expansion valve’s main job is to control refrigerant flow as it enters the evaporator coil. Improper refrigerant flow can cause the evaporator coil to freeze up. If you have a frozen evaporator coil, call for air conditioning repair.

Your outdoor AC unit naturally makes a certain amount of noise when it starts up or changes speeds. But if you notice hissing, whistling, banging, squealing, or clanging noises, you need to turn off the air conditioning and call for AC repair right away. 

A bad or failing expansion valve can also cause inconsistent airflow temperatures. The air might be cool one minute and warm the next. This can be due to the valve’s inability to control the refrigerant flow. If your AC is blowing warm air, call for HVAC repair. Your HVAC technician will troubleshoot the problem, as there are several things that can cause this issue.

In some cases, an electronic or TXV valve adjustment is sufficient. You should know that AC expansion valve replacement is not cheap. It takes about 4-6 hours of labor, and the part itself can cost several hundred dollars.  

A ballpark figure for a TXV valve replacement is $250-$2,000.  The total cost (parts and labor) will depend on system size, whether you need additional refrigerant (refrigerant recharge), if other repairs are needed, if the system is still under warranty, and more. Replacing an electronic expansion valve would run you about the same. 

If you have an older system that requires multiple repairs, you may want to consider HVAC replacement instead of pouring money into the system for repairs. Check out our Repair or Replace Guide for some tips.  

Keep in mind that some of these problems can be caused by multiple issues with your air conditioning system. An HVAC professional can get to the root cause and get your AC running normally again. If your system is 15+ years old and you have frequent repairs, they may recommend air conditioner replacement. 

Anne Fonda, Content Writer at Trane Technologies

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.

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