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Introducing the Thermostatic Expansion Valve

Your home’s HVAC system has many little gewgaws in it that, like any machine, must all do their own little job if the whole machine is going to operate properly. A bicycle won’t work if it doesn’t have a chain. A car won’t drive without a motor. Even a shopping cart isn’t much use if it’s missing a wheel.

The professional technicians at Rowland Air know all about thermostatic expansion valves and how to fix any related issues. 

What Is It and What Does It Do?

The thermostatic expansion valve is like a throttle. It’s like the gas pedal in your car or the volume knob on your entertainment system. In refrigeration and air conditioning, it is a crucial component that controls how much refrigerant gets injected into the system’s evaporator.

How It Relates to the Residential HVAC System

Your thermal expansion valve is one of four key elements in your HVAC system, which include:

  • Compressor
  • Condenser
  • Metering device (thermostatic expansion valve)
  • Evaporator

The basic refrigeration cycle is what makes air conditioning possible. The compressor compresses the refrigerant from a low-pressure gas into a high-pressure gas. As this happens, it absorbs heat. 

That gas passes into the condenser, which forces the refrigerant to cool rapidly due to contact with ambient temperatures in the coil. This rapid cooling makes the gas condense into a liquid. 

Still, under high pressure, this liquid then passes into the thermostatic expansion valve or metering device. What happens here is precisely the same thing that happens whenever you use an aerosol spray can. The rapid expansion of the pressurized liquid refrigerant as it passes through the metering device makes it really cold. 

Now a gas again, it travels on to the evaporator inside your home. This is where interior air passes over the evaporator coil, gets cooled, and passes through your home’s ductwork system.

How to Tell When It’s Gone Bad

The long and the short of it is that you won’t be able to tell when your valve has gone bad without a professional. There are a lot of symptoms to diagnose, including low evaporator pressure, low compressor amp draw, and other super-technical, sciency stuff.

The point is that it is often misdiagnosed, even by professional technicians. Even when thermostatic expansion valves that have been replaced are tested, up to two-thirds of them show no sign of failure. 

Adding to the challenge, the problem can disguise itself as a low airflow issue (pointing more toward the blower motor, a collapsed return duct, or a clogged filter) or low refrigerant levels. This one can be tricky indeed.

That’s why you need a professional technician. Rowland Air’s pros know how to evaluate the entire system, taking in all variables, to get the diagnosis right the first time. Only a professional with years of experience can do that for you. 

So the next time you need an HVAC pro, you can impress them by asking if they’d come to look at whether your TXV is bad. At that point, they’ll probably smile knowingly and say, “That depends.”