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Nissens: Thermal Expansion Valve Fault Guide

A faulty thermal expansion valve (TXV) will impact the air conditioning system’s performance and the life of the compressor, warns climate system specialist, Nissens.

A delay in the valve reaction or improper, unbalanced metering, along with the valve being stuck in an open or closed position, are among the most common faults of a malfunctioning TXV. These issues can also expose the AC compressor to excessive workloads, a shortage of lubrication or flooding, leading to severe damage.

Understand the symptoms of a faulty TXV and you can ensure you get the correct AC system diagnosis and carry out the required repair.

Here, Nissens provides some examples of TXV faults:

Improper metering of the refrigerant flow

Impaired metering failure often occurs in low-quality valves, high-mileage vehicles, through wear or by leaks within the power-sensing element of the valve, and improper setting of the valve’s superheat. It occurs when the valve’s primary control (power) element is out of the proper sensing and reaction settings.

Stuck valve

Most commonly, the problem has a root cause in impurities and debris inside the AC loop linked to the inappropriate use of additives for the AC system, a worn receiver-drier, particle formation after compressor seizure, or incorrect/lack of flushing. Depending on the position where the valve is stuck, there are several outcome scenarios, including a limited flow of the refrigerant.

Impurities and debris inside the TXV

AC system contamination, additives, a worn receiver-drier, particle formation following an AC compressor seizure and incorrect flushing may lead to inner valve blockages.

Severe AC compressor failure/seizure

Impaired lubrication caused by overheating, lubricant dilution or excessive impurities formation can all be linked to a faulty TXV.

Always replace the TXV when replacing an AC compressor, it is a relatively inexpensive add-on and can prevent severe failures. Always replace the valve if the system is diagnosed with severe contamination and after a compressor breakdown caused by seizure/overheating. Remember to flush the AC system before fitting the new compressor and replacement TXV.

Technical training, data and resources can be found at:

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