Functions of Thermostatic Expansion Valves in Heating and Air Conditioning Systems

Thermostatic Expansion Valves

The thermostatic expansion valve, also known as TXV, in an HVAC system is an adjustable restrictor. This part in heating and air conditioning systems controls the fluid that runs into the evaporator in heat pumps or central cooling systems. This allows the system to guide compressors’ coolant flow rate and pressure. The TXV is an essential part of a heating and air conditioning unit. When the evaporator is not under the required pressure, the thermostatic expansion valve brings in more fluid till it reaches an equilibrium. This will give you a balanced system that cools your home with minimum energy consumption.

Some Misconceptions About TXV in Heating and Air Conditioning Systems

The primary role of a TXV in heating and air conditioning systems is to control the fluid; liquid refrigerant flows into the evaporator. Some individuals assume that it performs other functions. As assumed, the TXV does not control air temperature, capacity, humidity, head pressure, etc. TXV cannot be used to control any other parts of the system. It would only lead to poor performance or system failure. Ensure you contact a technician if you are unsure about any HVAC system adjustments.

How TXV Functions with Other Parts of the HVAC System

The primary component of the HVAC is the compressor, condenser, and evaporator. Other pieces build up the steady functioning of an AC. However, there would be no refrigeration loop without the compressor, condenser, and evaporator. In addition, the loop cannot work if there is no regulation from the TXV. 

A diaphragm in the TXV opens and closes the valve, regulating the amount of liquid flow into the evaporator. When your home does not require cooling, the TXV gets more fluid into the evaporator to increase pressure on both sides of the compressor. This will help to get more heat through it. When it is time to cool your home, the TXV reduces the flow of hot fluid into the evaporator till when everything gets cool again. Professionally, you are advised to refrain from trying to service your TXV yourself, no matter how simple it may look.

Does the Thermostatic Expansion Valve Fail?

Systems and parts are bound to fail. Refrain from getting surprised when you notice your TXV is not functioning as expected. Cases of failed TXV can be traced to the diaphragm. This part of the TXV is thin and weak. The pressure inside the evaporator can get higher than the outside pressure when the gas stream is very hot.

This could cause the fluid to blow through the expansion valve. Ruptures in the small tubes can cause the diaphragm to blow. The tubes are the passage through which the refrigerant goes in and out of the TXV. When the diaphragm gets blown out, there would be a loss of refrigerant from the air conditioning system. Call an HVAC technician when this happens.


Adjusting a TXV is not advised. If you notice your TXV malfunctions, call a professional to either repair or replace it. A pressure test gauge and an infrared scanner diagnose faulty TXV. Aside from that, diagnosing services are cost-effective, and this role ensures that your AC refrigerant charge is balanced. You may need to change the thermostatic expansion valves in heating and air conditioning systems when you discover that the refrigerant has dropped below, keeping your space cool.