What Is a TXV Thermal Expansion Valve?

A thermal expansion valve (TXV) is a component of an air conditioning system which can often be the source of your system working inefficiently.

It is part of the system which regulates the rate at which refrigerant flows into the evaporator. It also prevents refrigerant from returning back into the compressor.

If the valve isn’t working properly and fails to do this, or becomes inefficient at doing it, there won’t be enough refrigerant in the evaporator to blow out cool air. The householder will notice the temperature of their home is higher than the temperature on the thermostat.

TXV Troubleshooting

Often the TXV expansion valve will be working fine, and other parts may be the cause of the problem. If there isn’t enough refrigerant in the evaporator this may be because there isn’t enough pressure in the suction line leading to the TXV’s diaphragm. When this occurs, the valve won’t open enough, or maybe even at all.

If the refrigerant hasn’t cooled enough to return to liquid, it won’t put pressure on the valve. This malfunction may be due to a lack of subcooling, or flashing.

As the cause of the problem could be a number of issues, the engineer will need to troubleshoot the system thoroughly by checking:

  1. Superheat (by calculating the pressure and temperature of the liquid going into the valve)
  2. Subcooling (if the subcooling is too high, there may not be enough refrigerant)
  3. the valve is connected to the suction line properly
  4. the bulb, which senses temperature, is fixed in the right position
  5. if there is any dirt or debris in the valve


A diagnosis of the problem, following a thorough check of the system, may identify a part which has become worn or has broken and needs replacing, the valve may be leaking refrigerant, or the system may need to be cleaned to remove debris.

If the valve needs replacing, a qualified engineer should undertake the TXV installation as many potentially hazardous materials are involved. You may come into contact with refrigerant, which is a pollutant, and must be handled responsibly.

In addition a qualified engineer will be able to carry out the TXV installation to a professional standard, which will prolong the life of the thermal expansion valve. In turn, this will ensure your air conditioning system will continue to work efficiently.

Inexpertly installed equipment can cause greater damage to your air conditioning system than the original fault.

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