How to Determine if a Car AC Expansion Valve is Good or Bad?
2 Answers
You can judge the condition of a car AC expansion valve by the expansion pressure. If the high pressure is very high and the low pressure is very low, the expansion valve is faulty. Below are the fault causes: 1. Expansion valve blockage: Symptoms include higher temperature at the car's AC vents, lower pressure on the high-pressure side, and negative pressure on the low-pressure side. For minor blockages, frost or condensation will appear at the inlet end of the expansion valve; for complete blockages, there will be no temperature difference between the inlet and outlet of the expansion valve. 2. Expansion valve opening too small or malfunctioning: The symptoms are the same as blockage faults. 3. Expansion valve opening too large: Symptoms include higher temperature at the car's AC vents and higher pressure on the low-pressure side.
I've worked in auto repair shops for over a decade, and the condition of the expansion valve directly affects the AC cooling performance. If the expansion valve is clogged or worn out, the car's AC will produce noticeably weaker cold air or may not blow cold air at all. When diagnosing, the first step is to activate the AC system and observe the high and low-side pressures: a properly functioning expansion valve should maintain balance; if the high pressure rises while the low pressure drops, or vice versa, it indicates a potential fault. Then listen for sounds: abnormal expansion valves often produce a hissing noise—don't overlook this detail. Another practical tip is to check refrigerant flow: use a transparent sight glass or professional tools to observe if the refrigerant flows evenly; if it's irregular or shows heavy frosting, the valve is likely clogged. A reminder: refrigerant is hazardous, so don’t attempt DIY fixes—it’s best to take the car to a certified repair shop for a thorough inspection using diagnostic tools to check the compressor and the entire system. Regular maintenance, such as cleaning the AC filter, can reduce the risk of expansion valve clogging.
