Air conditioning systems are often located in homes and vehicles. There are many components to an air conditioning system, including the compressor, condenser, evaporator and thermal expansion valve, or TXV. A thermal expansion valve causes the air conditioner to operate more efficiently. A faulty valve may cause your air conditioner to work harder, resulting in possible damage to other components. The first step in troubleshooting or replacing a thermal expansion valve is knowing its location.

What Is a TXV?

The thermostatic expansion valve is a device that is used in some air conditioners to make the unit operate more efficiently. The expansion valve does this by making sure that the air conditioner evaporator has the correct amount of refrigerant liquid. Too little refrigerant may cause the air conditioner to work harder to cool the air. Too much refrigerant in the system may collect in the bottom of the input line to the evaporator.


The evaporator is an essential part of an air conditioner. The evaporator converts liquid refrigerant into a gas. Compressed refrigerant leaves the air conditioning compressor extremely hot. The fins of the condenser cool the fluid before it enters the evaporator. The evaporator changes the cooled liquid from the condenser into a very cold gas.

TXV Parts

The thermostatic expansion valve houses a thermostat that is controlled by a spring. The spring pushes a diaphragm up or down as needed to provide the correct amount of refrigerant liquid to the evaporator. A small tube connects a bulb to the expansion valve housing. The bulb is mounted to the output line from the evaporator. The bulb detects the amount of heat in the output line and the thermostat adjusts the diaphragm so that the correct amount of refrigerant enters the evaporator through the input line.

TXV Location

The thermostatic expansion valve is usually mounted inline with the tube that supplies liquid coolant to the air conditioner evaporator. The bulb of the expansion valve is mounted to the outside of the output line of the air conditioner evaporator. The bulb should be mounted to the top of the output line, as mounting it to the underside of the line can give false readings to the expansion valve and cause it to malfunction. This may be caused by oil lying in the bottom of the output line.