Servicing TXV Valves

What is a Thermal Expansion Valve?

Thermal expansion valves, or TXV/TEV valves for short, are valves which control the flow of refrigerant into the evaporator. TEV valves are essential for energy-efficient operation of modern 13 SEER systems because they keep the refrigerant closer to the optimum superheat at all operating conditions.

TEV valves are often viewed as mysterious, esoteric, devices whose operation is understandable only to those with years of experience. This is absolutely not the case. The TEV valves sole function is to precisely control the flow rate of refrigerant into the evaporator at the same rate it evaporates. That’s all.

Troubleshooting TEV Valves

There are three main issues that can occur with TEV valves: starving, flooding, and hunting. Each have their own symptoms and are fairly straight forward to diagnose and treat. Let’s examine the symptoms.


Starving is when the refrigerant feeding the evaporator is evaporated before it ever reaches the evaporator coil. This results in high superheat, higher than desired load temperatures and low suction pressure.


Flooding occurs when the TEV valve is releasing more refrigerant than what can be evaporated in the coil. This will allow liquid to enter the compressor and possibly result in noisy operation or a frosted compressor cover. Other symptoms include low superheat and higher than normal suction pressures.


Hunting is when the TEV valve fluctuates back and forth between starving and flooding, alternately releasing too much or too little refrigerant. Symptoms of this include wildly variable superheat, and a combination of flooding and starving symptoms.

Diagnosing and Fixing TEV Valve Issues

Isolating the causes of hunting, flooding or starving is something that is more involved than what the average homeowner could, or should, attempt to diagnose and fix on their own. Your HVAC system is a delicately balanced group of machines all working together in harmony to generate cold or heated air. Small disruptions or changes in variables can have drastic effects on the operation of your HVAC system. If you think your TEV valve needs adjustment or replacement, give us a call to schedule a service call!

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