What Is a Thermal Expansion Valve?

Published on: July 19, 2013

The basic principles of refrigeration are used to make air conditioners cool and heat pumps cool as well as heat. An air conditioner cools by routing a refrigerant under pressure through tubing for transfer of heat. First, refrigerant is routed through the compressor which heats and pressurizes it. The highly pressurized gas is routed through tubing to a condenser that dissipates the heat and sends it in liquid form under high pressure to the evaporator. Here, the pressure drops and the liquid evaporates as it picks up heat. It returns to the compressor as a low-pressure gas. An expansion valve located between the condenser and evaporator regulates both the temperature and amount of refrigerant that is sent to the evaporator.

The continuous circulation of refrigerant through the system removes heat and produces cooled air. Heat pumps have a valve that allows refrigerant to run either direction so that a unit can either heat or cool. In air conditioners, refrigerant flows in only one direction.

What an Expansion Valve Does

The change in pressure of the refrigerant causes the conversion of liquid to gas. During this process, the refrigerant absorbs heat, which cools the evaporator coil. Both the amount and the temperature of refrigerant flowing through the system must be regulated. This is done by an expansion device. Two types of control devices are used on air conditioners: thermostatic (often called thermal) expansion valves and capillary tubes.

Capillary tubes are rigid and cannot adjust to changes in load. Capillary tubes work well in environments with little temperature change. When ambient temperatures fall below or rise above recommended levels, capillary tubes lose up to 85 percent efficiency. They are, however, inexpensive and simple to operate.

Thermal expansion valves (TEV) have several advantages over capillary tubes. They contain movable parts that adjust to changes in temperature and volume of refrigerant. The TEV meters the flow of refrigerant, ensuring more accuracy in both volume and temperature. If a system is overcharged (too much refrigerant), higher pressure causes overheating and makes the compressor run longer. If the system is undercharged, not enough refrigerant is under pressure to achieve the desired temperature, which also makes the compressor run longer.

How a Thermal Expansion Valve Works

A thermostatic expansion valve controls the amount of refrigerant that flows to the evaporator to maintain a constant supply of superheat. By metering the flow of refrigerant, a TEV helps to maintain the pressure difference between the compressor and evaporator. The TEV restricts the flow rate of refrigerant to raise the pressure on the compressor (high) side and drop the pressure on the evaporator (low) side. It is placed between these two elements of the unit to separate and monitor the pressure systems on either side.

A TEV has several parts: a sensor bulb, a needle valve operated by a spring, a diaphragm and tubing that enters and exits the device. The temperature-sensing bulb filled with a gas monitors temperature change. As temperature increases, so does pressure. As refrigerant enters the device, the pressure pushes the spring against the diaphragm. The pressure of the diaphragm makes the needle adjust to the amount of pressure. With more pressure, the needle is lowered and allows more liquid to pass to the evaporator. More fluid entering the evaporator lowers the temperature by absorbing more heat.

Expansion valves are preset at the factory for optimum performance. In some situations, settings may need to be adjusted based on the specific conditions at your site. A heating, ventilation, air conditioning and refrigeration professional is trained to monitor and adjust expansion valves so that your equipment works properly.

Maintaining Your Air Conditioning System

All components of an HVAC unit must be properly calibrated for best performance. Heating and air conditioning professionals can help you maintain your system. Most manufacturers recommend seasonal tune-ups to ensure that all elements of a system function properly. Checking refrigerant levels, ensuring that the unit cycles on and off properly and cleaning evaporator and condenser coils are part of this service. Minor seasonal adjustments lessen unwanted repairs, prolong the life of the unit and increase energy efficiency.

AC Southeast®

AC Southeast® serves communities in Alabama, Florida, Georgia, Mississippi and South Carolina. Our affiliated heating, ventilation and air conditioning (HVAC) contractors are located throughout this five-state area to serve you quickly and efficiently. These highly trained professionals are properly licensed to work in each state. Technicians are certified in core competencies and specialties through North American Technician Excellence (NATE), the HVAC and refrigeration industry standard for testing and certification.

We offer the following services:

  • Scheduled maintenance and annual tune-ups
  • Bryant and Carrier Factory Authorized Dealers
  • Home energy analysis
  • Residential and commercial services
  • Installation and repair of all makes and models of heating and cooling equipment
  • Attractive financing for new installations
  • Energy Star rated products
  • Licensed, insured and bonded
  • Written estimates before starting work
  • 24-hour emergency service

Being a Factory Authorized Dealer means that we adhere to the stringent business practices required for this prestigious designation. Customer satisfaction is top priority, with 100 percent customer satisfaction guaranteed.

If you require new installation, the contractor will conduct a detailed analysis to recommend equipment suitable for your site conditions. It is important to accurately calculate the amount of load required to keep your indoor environment comfortable. An undersized unit makes the compressor work harder to cool the rooms. An oversized unit will reach the target temperature and cycle off before removing the appropriate amount of moisture from the air. This creates a clammy feeling indoors.

Carrier and Bryan products installed by our Factory Authorized Dealers include warranties and guarantees on equipment, parts and labor.