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 thermal expansion valve (TXV), experts at Nissens say.
These factors can also expose the AC compressor to excessive workloads, a shortage of lubrication or, conversely, flooding, leading to severe damage.
It is therefore important for technicians to understand the symptoms, to ensure they are in a position to make the correct AC system diagnosis, in order to affect the correct repair, which is why Nissens is dedicated to providing them with the technical knowledge to allow them to do so.
Improper metering of 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.
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 improper/lack of flushing procedure.
Depending on the position where the valve is stuck, there are several outcome scenarios, including a limited flow of the refrigerant.
Impurities and debris concentration inside TXV
AC system contamination, additives, a worn receiver-drier, particle formation following an AC compressor seizure, improper flushing – all of which 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.
It’s advised that the TXV is always replaced when undertaking AC compressor replacement, as it is a relatively inexpensive add-on, which can prevent severe failures.
Always replace the valve if the system is diagnosed with severe contamination and after the compressor breakdown caused by seizure/overheating.
Remember to flush the AC system before fitting the new compressor and replacement TXV.
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