Causes Of Air Conditioner TXV Malfunction

An air conditioner (AC) has several critical parts that must work well for the AC to cool the house effectively. The thermal/thermostatic expansion valve (TXV) is one of these parts. Below are some reasons the TXV might malfunction. 

Improper Sizing or Installation

The TXV controls the volume of refrigerant that flows into the evaporator. The evaporator contains a refrigerant that absorbs heat inside the house and dumps it outside, effectively cooling your house. The AC's capacity determines how much refrigerant it needs to cool the house.

Improper TXV impairs the AC's cooling efficiency. For example, an undersized TXV might underfeed the evaporator with refrigerant, reducing heat absorption. Reduced heat absorption leads to reduced cooling efficiency.

The installation of individual TXV components also affects its function. For example, the TXV has a bulb that connects to the evaporator's coil suction line to sense the refrigerant's temperature. A loose or incorrectly placed sensing valve might sense the wrong temperature and interfere with the valve's functions. 


Dirt or debris can accumulate inside the valve and block refrigerant flow. Restricted refrigerant flow means the evaporator coil won't receive the refrigerant to absorb heat efficiently and cool your house. Inefficient cooling also increases the AC's wear and tear and energy consumption.

Clogging can also increase refrigerant pressure inside the TXV valve. The extreme pressure increases can damage the refrigerant lines, leading to refrigerant leakage and compromising AC performance. Refrigerant leaks are also dangerous since the fluid is poisonous and can compromise your family's health.

Improper Valve Adjustment

You adjust the TXV for precise control of refrigerant flow. The adjustment involves setting the valve's spring or diaphragm position, depending on the desired refrigerant flow or cooling load. Improper valve adjustment can lead to refrigerant underfeeding or overfeeding, just like clogging does. As such, improper adjustment and clogging have similar effects.

Temperature Sensor Failure

The TXV uses a temperature sensor, typically a bulb or capillary tube, which detects the refrigerant temperature. The TXV uses the sensor's feedback to adjust the valve's opening and refrigerant flow. For example, if the sensor detects high temperatures, the valve will open wider to allow more refrigerant flow and increase cooling.

Temperature sensor damage leads to improper temperature readings and impaired cooling. Accumulated wear and tear, accidental mechanical damage, and electrical problems are common causes of temperature sensor damage.

The TXV is a sensitive AC part and requires professional service, adjustment, or repair. Contact a local air conditioning repair service to learn more.