Why does the expansion valve frost up? How to diagnose the malfunction
21 Nov,2025
In the practice of refrigeration equipment maintenance, observing the frost formation patterns on the expansion valve has become a core diagnostic tool for technicians to assess the system's operational status. This seemingly simple physical phenomenon actually carries rich insights into how the system is running—when high-temperature, high-pressure liquid refrigerant passes through the expansion valve and undergoes throttling to reduce pressure, the sudden drop in pressure triggers an intense vaporization process that absorbs heat, causing the valve body's surface temperature to plummet. If the ambient temperature remains higher than the valve's surface temperature, frost will begin to form. Different frost patterns serve as the system's "vital signs monitor": for instance, comprehensive frosting across the entire valve body may indicate insufficient refrigerant flow or a clogged filter screen, while localized frost on the outlet side could point to either excessive refrigerant or an abnormal opening of the expansion valve.
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