A thermostatic expansion valve (TXV) is an adjustable restrictor. It controls the fluid that flows into the evaporator in a central cooling system or heat pump. This enables the system to control the coolant flow rate and pressure in the compressor.

The compressor pushes the coolant, or refrigerant, through the condenser to the evaporator. When the heat from a home or business passes over the fins of the evaporator coil, more fluid evaporates into a gas. This temperature-sensitive gas starts to heat up and expand in the evaporator. As more fluid evaporates, the pressure on the compressor increases. As this happens, the heat from your home or business transfers to the coils in the condenser. An internal fan will help blow warm air from the inside of your home or business over the evaporator coils. This process transfers heat from inside your home or business to the outside, cooling the building down.

As the gas temperature in the evaporator rises, pressure against the compressor increases. This is where a TXV comes into play. The TXV has a diaphragm that expands and contracts with temperature changes. That allows it to regulate how much fluid gets into the evaporator. The amount of fluid entering the evaporator coil balances the pressure on the compressor. Since it can measure and regulate how much fluid enters, it does so at a slow rate. When the evaporator is not under enough pressure, the TXV will bring in more fluid until it reaches an equilibrium. As a result, you will have a balanced system that can cool your home or business with the least energy input.

Common Misconceptions About a TXV

As you may have noticed, the thermostatic expansion valve has only one responsibility. Its role is to control how the liquid refrigerant flows into the evaporator. Some people assume that it performs more functions. It does not control head pressure, capacity, air temperature, humidity or suction pressure as most people assume. Do not use the TXV to control any other system variables because it will lead to poor performance. In some cases, it may cause a system failure. If you are unsure about any system adjustments, contact a technician.

How Does a TVX Work With Other Components?

The main components of an air conditioner are the compressor, the condenser and the evaporator. The compressor draws in low-pressure liquid refrigerant. It compresses this into a high-pressure gas. The gas then circulates through the condenser. An internal fan blowing air over the coils will cool the refrigerant. As the high-pressure gas cools down, it condenses back into a liquid. The heat moves outside your home or business via the dissipating fins on your condenser coils.

The expansion valve decreases the pressure of the coolant, allowing it to expand and change its state from a liquid to a gas in the evaporator. Before entering the expansion valve, the liquid coolant is quite warm, and upon leaving, it is very cold. This is not actually because the valve removes the heat; it’s because the pressure is decreased. The molecules of the refrigerant spread out as the substance exits the expansion valve’s orifice. A diaphragm in the TXV moves, opening and closing the valve and regulating how much liquid flows into the evaporator.

When your home or business does not need cooling, the TXV allows in more fluid. This increases pressure on both sides of the compressor, pushing more heat through it. As your home or business generates more heat, the demand for cooling increases. The TXV slows down the rate of hot fluid flow into the evaporator until everything is cooled off again.

Several pieces make an AC work, but there would be no refrigeration loop without the compressor, condenser and evaporator. Furthermore, that loop would not function without regulation from the TVX. For this reason, you should never try to service your TXV, even if it’s a simple adjustment.

Does the TXV Sometimes Fail?

Like any other system, the TXV is not immune to failure. At some point, you may notice the TXV is not performing as expected. Many cases of failure in a TXV can be linked to the diaphragm.

The diaphragm in a TXV is very thin, which makes it weak. If the gas stream becomes too hot, the pressure inside the evaporator can become greater than the outside pressure. In this case, the fluid can blow through the TXV. The diaphragm blows because of a rupture in one of the small tubes. These tubes carry the refrigerant to and from the TXV. There is no way to stop the loss of refrigerant from your air conditioning system when this happens. You will have to contact an HVAC technician to repair it.

Can You Adjust the TXV?

Manufacturers do not recommend adjusting the TXV. If your system’s TXV is malfunctioning, only a professional should attempt to repair or replace it.

Why Do People Often Misdiagnose the TXV?

A problem with the TXV is sometimes misdiagnosed because the device operates automatically. If the air conditioning doesn’t seem to be cooling your home or business, the first thing a technician will do is check your thermostat to ensure that it is working properly.

If you have an older wall-mounted thermostat, the technician may check your premises for air leaks. If you have a newer programmable thermostat, they might ask you to hold down one of the buttons while turning on the system. After these checkups, the technician may conclude either that the TXV is faulty or that something is wrong with the refrigerant in your system. The technician will then need to check the pressure of the refrigerant and air conditioner lines. These must be eliminated before determining that a TXV malfunction is to blame.

What Is the Best Way to Diagnose a TXV?

A good technician may diagnose a faulty TXV using a pressure test gauge and an infrared scanner. In addition to this diagnosis being cost-effective, it ensures your air conditioning system’s refrigerant charge remains balanced.

Common Signs That Your System Needs a New TXV?

If your air conditioner is blowing warm air, it can signify that the refrigerant has dropped below the minimum level to keep your space cool. Also, you may notice you need to add more refrigerant in the spring when you turn on your air conditioning for the season.

What Happens If There Is a Refrigerant Leak?

A refrigerant leak results in the loss of your air conditioning system’s coolant. It can occur when the diaphragm inside a TXV ruptures. This loss of coolant causes the air conditioner to work harder, making it run hotter and burn more electricity or gas. If the refrigerant is low but there are no leaks, an HVAC technician can add more to balance out your system. If you have a leak in your system’s lines or from the TXV, a professional must repair it.

Make sure you get a qualified technician to handle your TXV. At AC by J we have an expert team of trained and certified personnel who perform heating and cooling installation, maintenance and repair. You can also depend on us for any of your plumbing needs from water treatment to pipe replacement. We’re locally owned and operated, and we’ve been serving Scottsdale and the entire Phoenix Valley since 1983. Call us at AC by J today to make an appointment for quick and reliable services!

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