What Is a TXV Valve in HVAC? A Complete Guide
Introducing the master of your AC refrigerant
Highlights
The TXV regulates how much refrigerant can flow into the evaporator coil to start a cooling cycle in home air conditioning systems.
Since TXV are sensitive and complex AC components, you should always hire an AC repair pro to inspect them.
TXV replacements can cost between $350 and $450, but additional labor and new refrigerant can lead to higher costs.
Most home HVAC systems, including heat pumps, use TXVs, but they are being replaced by more accurate EXV or electronic expansion valves.
The inner workings of your air conditioning system don’t have to be mysterious. One of the most obscure components is a TXV in HVAC systems, which are small, complex parts known as the thermal expansion valve. This valve connects to your AC’s evaporator coil and helps regulate refrigerant. Don’t worry, you can hire an AC installer to repair and replace it, but in the meantime. we’ll break the ins and outs of TXVs for you.
What Is the TXV in HVAC?
The thermal expansion valve (TXV) controls the amount of refrigerant released into the evaporator section of your HVAC system at any given time.
This essential component is connected to the top of the evaporator coil and controls how much refrigerant can enter. It’s a lumpy valve, made of copper or the same metal as the evaporator coils, sporting a cross-section of one larger, circular end and one smaller, capped end. It’s very recognizable and easy to spot.
The THX valve regulates how much of the cooled liquid refrigerant enters the evaporator coil to start (or restart) the cooling cycle. It’s job is to ensure there isn’t not too much refrigerant in the coil, but enough to easily absorb heat and turn it into gas. If there’s too much refrigerant in the evaporator coil, it won’t be able to properly absorb the heat and expand, and the air conditioner won’t cool the air. Plus, this mistake could force liquid refrigerant downline where only gas refrigerant is supposed to go. If the TXV doesn’t let in enough refrigerant, there won’t be enough to absorb significant heat.
How Does the TXV Work in HVAC Systems?
The TXV valve regulates refrigerant flow in an air conditioning system, interacting with the evaporator coil—a heat-conducting assembly of pipes and fins inside the indoor unit. Refrigerant, which is a heat-absorbing fluid, cycles through these pipes, absorbing indoor heat as air passes over the coil, then turns to gas.
Then, the gas is compressed in the outdoor unit. The heat flows into the outdoor air, the refrigerant cools down again, and it moves back into the house to repeat the cycle. Unlike continuous flow, which is inefficient, the TXV valve adjusts refrigerant flow based on current temperatures and pressure, ensuring optimal efficiency and preventing issues. The TXV has a clever design that uses the current heat limits and pressure of the refrigerant as automatic regulators to only let the right amount inside.
Important Components of TXV in HVAC
The THX valve works to regulate refrigerant flow with as few moving HVAC parts as possible to avoid wear and tear. These systems help control the “superheat” of the refrigerant. Superheat refers to how much heat the refrigerant can absorb beyond its saturation temperature or the point when it turns from a liquid into a gas.
We won’t get too technical (you aren’t earning your HVAC certification), but here are the most important TXV components and how they work together.
Diaphragm: The diaphragm opens and closes the valve, letting refrigerant pass through to the evaporator coil when it is open. Various pressures exert themselves against the diaphragm to push it open or closed based on the conditions of the AC refrigerant.
Sensing bulb: The sensing bulb sits at the power element head and measures suction pressure by comparing the AC refrigerant’s state to a refrigerant sample in the bulb.
Setting spring: This spring also exerts pressure on the diaphragm and can be manually adjusted. This is one of the most important jobs of the HVAC technician when adjusting refrigerant and making evaporator coil repairs.
Evaporator connection: The connection to the evaporator helps measure the current pressure of the refrigerant already inside the coil, which also counters the diaphragm. Between the counteracting forces, the diaphragm only opens when it needs to.
TXV and Refrigerant Types
Remember how the TXV sensing bulb uses refrigerant to help compare pressure differences? That refrigerant isn’t always the same as the refrigerant the evaporator coil uses. TXVs often have two refrigerant ratings, one for the refrigerant it uses in the bulb and one for the refrigerant it manages in the air conditioner.
Internal and External Equalization
TXV can use internal or external equalization, which applies to how the valve senses pressure from the evaporator coil. Internal equalization senses evaporator coil pressure at the outlet of the valve, which is the simplest method and used in most systems. External versions use a separate connection to sense pressure from an equalizer line, which senses pressure changes in larger, more complicated HVAC systems.
TXV Alternatives
Most home HVAC systems have TXVs. Even cooling systems in window AC units and refrigerators have their versions of a TXV. In rare cases or older cooling systems, the air conditioner may use a piston-like design that pumps only a limited amount of refrigerant into the evaporator coil. It’s a much simpler system with fewer delicate parts, but it’s not nearly as accurate as a TXV, leading to efficiency problems.
There are also newer solutions for the latest HVAC systems, like electronic expansion valves (EXV). EXVs use very simple motors and pressure sensors to create a pressurized chamber that controls the flow of the refrigerant based on its state and the amount in the evaporator. EXV valves are more durable and accurate than TXVs, and will likely replace them in the future. For now, they’re only found on newer and more expensive AC units.
Signs the TXV Needs Repair
Since the TXV controls how well the AC unit operates, a bad one can cause several problems, making it hard to narrow down the cause without a professional inspection. Signs you may need an HVAC inspection include:
AC blowing warm air or struggling to heat: If the air conditioner can’t produce cool air or is running non stop to cool down the home, it’s a common sign of refrigerant problems and related issues.
Old, untended system: As refrigerant grows lower and gets dirty throughout the years, it’s more likely to jam or wear down the TXV, creating more problems. That’s why it’s a good idea to check your refrigerant levels every few years.
Frozen coils: Frozen evaporator or condenser coils is another sign that the refrigerant isn’t absorbing heat properly in the cycle. It can be caused by a defective TXV.
Visible grime or wax buildup on the TXV: A dirty TXV can be a sign that the valve is jammed and has other issues. Hire an AC repair technician to clear up the grime or wax buildup.
DIY vs. Hiring a Pro
While the TXV valve is a relatively small part of an indoor AC unit, it’s also one of the most complex. Homeowners should avoid trying to remove, adjust or tamper with the TXV. It could cause serious problems or prevent your AC from cooling effectively.
Instead, we highly recommend contacting a professional air conditioning installer or repair service near you if there’s an issue with the TXV or refrigerant. A TXV repair or replacement costs around $350 on average. Since the TXV valve is a complicated component and requires specialized work like “pumping down” the refrigerant into a storage tank while working, costs may range higher than average. That’s especially true if the technician recommends replacing all of your refrigerant along with the new valve. Refrigerants can grow contaminated over the years, so it’s often a good idea to replace it along with your TXV so both components start fresh. Common R-22 refrigerants cost between $300 and $960 to replace.
Frequently Asked Questions
Yes, heat pumps have TXVs. Heat pumps are very similar to air conditioners but they reverse the process and take heat from the outdoors to heat a home inside. That means heat pumps require slightly different components and may use different refrigerants. However, they also have evaporator coils and usually TXV s to accompany them. Like with AC, the TXV must match the heat pump system.
It’s possible, but not guaranteed. If your old TXV was faulty for a long time, a new one may increase your home’s energy efficiency and cause your energy bills to drop. If your AC uses one of the older methods like pistons to control refrigerant, upgrading to an entirely new system with a more advanced valve will likely save money on bills because of multiple new efficiencies.
This term references a “quick fix” for a TXV with a broken power element. This trick is where a technician puts a dime or similar conductive coin between the valve and power element to help the power element work while the technician finds and installs a new TXV valve. This trick is largely apocryphal and unlikely to work in most cases. Never try to do it yourself: Leave the TXV fixes to professionals.