How to Determine Expansion Valve Failure?
2 Answers
Under standard refrigerant charge and engine idle conditions, the low-pressure side of a typical car's 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. Below are additional relevant details: Introduction to Expansion Valves: The expansion valve is a critical component in refrigeration systems, typically installed between the liquid receiver and evaporator. It converts medium-temperature, high-pressure liquid refrigerant into low-temperature, low-pressure wet vapor through throttling. The refrigerant then absorbs heat in the evaporator to achieve cooling. The expansion valve controls flow rate based on superheat changes at the evaporator outlet, preventing insufficient evaporator area utilization and compressor slugging. An ideal expansion valve should dynamically adjust its opening degree according to evaporator load variations to regulate flow. How to Evaluate Expansion Valve Performance: Due to thermal inertia in the temperature sensing bulb's response, expansion valves always exhibit delayed reactions. If plotted on a time-flow diagram, the valve's performance curve appears as a jagged line rather than a smooth curve. The quality of an expansion valve is reflected in the amplitude of these fluctuations - larger amplitudes indicate slower response times and poorer valve quality.
I've been driving for several years, and my car's air conditioning always acts up during summer. The AC suddenly stops cooling, with only a slight cool breeze coming from the vents, and after a while, the car feels stuffy and uncomfortably hot. I listened carefully and could hear hissing or clicking noises near the compressor, which was quite annoying. Later, I took the car to the repair shop. The mechanic used a pressure gauge to test the high and low-pressure systems and found that the high-pressure side was too high while the low-pressure side was too low, indicating restricted refrigerant flow. He also disassembled the AC lines to check if the expansion valve's core was stuck or clogged with debris. I remember how the cooling was restored to like-new after that repair. A faulty expansion valve can really cause trouble, and regularly cleaning the AC filter can help prevent such issues.
