How to Determine if the Expansion Valve is Faulty?
2 Answers
Under standard refrigerant charge and with the engine idling, the low-pressure side of a typical car air conditioning system should read between 0.1-0.25MPa (1-2.5KG/CM2 or 15-35Lbf/in2). If the low-pressure reading falls below or exceeds this range, it indicates a malfunctioning expansion valve. Here are detailed insights about the expansion valve: 1. Working Principle: After passing through the condenser, high-temperature and high-pressure refrigerant undergoes pressure and temperature reduction when flowing through the expansion valve, transforming into low-pressure, low-temperature liquid refrigerant. This process creates optimal conditions for refrigerant evaporation and cooling within the evaporator. 2. Primary Function: The expansion valve throttles and reduces the pressure of high-pressure liquid refrigerant from the dryer, while regulating and controlling the amount of liquid refrigerant entering the evaporator. This adaptation to varying cooling loads prevents compressor liquid slugging.
With over 20 years of experience in auto repair, diagnosing expansion valve issues starts with observing AC performance. If the air isn't cold enough when the AC is on, or if it fluctuates between cold and hot, that's a red flag. It's best to use pressure gauges to measure high and low pressure values: abnormally high low pressure may indicate the expansion valve is opening too much, while excessively low pressure suggests a blockage. Then check the temperature difference between the evaporator's inlet and outlet—normally around 5-8°C. If the outlet feels frosted or the temperature difference is off, the expansion valve is likely malfunctioning. Once, a customer's AC compressor kept making a clicking sound, and upon inspection, we found the expansion valve was stuck, causing refrigerant flow issues. Don't delay fixing such problems—a faulty expansion valve can damage the compressor.
