Hansberger Refrigeration Blog: Your AC Repair Resource

How a Thermostatic Expansion Valve Affects Your HVAC System

thermostatic expansion valveHave you given much thought to your thermostatic expansion valve (TXV) lately? As summer approaches, it’s a good idea to be aware of the function of this vital component in your central air conditioner. The TXV controls the temperature and flow rate of refrigerant that continuously circulates through the air conditioner as it absorbs heat from the house at the indoor evaporator coil before dispersing that heat at the condenser coil outdoors.

Where’s My TXV?

The thermostatic expansion valve is located near the AC indoor evaporator coil and adjusts the flow of refrigerant before it enters the coil. The basic sequence goes like this:

  • Refrigerant flow reaching the thermostatic expansion valve is under high pressure and moderately warm.
  • A sensing bulb at the evaporator coil senses pressure and temperature of refrigerant flowing through the coil.
  • The sensing bulb continuously adjusts the TXV to control the volume of refrigerant flow into the evaporator coil based upon the cooling requirements of the unit.
  • The flow of refrigerant from the TXV depressurizes rapidly as it enters the evaporator, and the refrigerant temperature drops precipitously. This process constantly keeps the evaporator coil cold to ensure efficient extraction of heat from warm indoor air passing through the coil.

When a Good TXV Goes Bad

A defective TXV may result in a number of symptoms, including warm air instead of cool air coming out of vents, ice or frost forming on the evaporator coil, short-cycling (the unit turns on and off rapidly or runs continuously without stopping), and an unexplained increase in cooling costs. A valve may fail from wear and tear after years of operation, or it may become clogged with some foreign matter present in the refrigerant flow.

What Comes Next?

In all scenarios, removal of the valve will be required and, in most cases, the most cost-effective option is to replace the existing valve rather than attempting to repair it. Because refrigerant must be removed from the system, the job must be performed by a licensed, professional HVAC technician.

For professional diagnosis and replacement of the thermostatic expansion valve, contact Hansberger Refrigeration and Electric Company.