How to Determine Expansion Valve Failure?
3 Answers
Under standard refrigerant charge and engine idling conditions, 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 falls below or exceeds this range, it indicates an expansion valve malfunction. Below is more relevant information: 1. Introduction to Expansion Valves: The expansion valve is a crucial component in refrigeration systems, usually 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 utilization and compressor slugging. An ideal expansion valve should dynamically adjust its opening to control flow according to evaporator load changes. 2. How to Evaluate Expansion Valve Performance: Due to thermal lag 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 zigzag line rather than a smooth curve. Valve quality is reflected in the amplitude of these fluctuations - larger amplitudes indicate slower response and poorer quality.
As a veteran driver with over a decade of experience, I've encountered quite a few cases of expansion valve failure. The most obvious sign is when the AC suddenly stops cooling, turning the car interior into a sauna. When the engine is running, you can hear a hissing noise, especially noticeable when the AC kicks in. Check the high and low pressure pipes - if there's minimal temperature difference, it indicates restricted refrigerant flow. I once almost got heatstroke during a summer trip, only to find out at the repair shop that the expansion valve was clogged. Replacing the component solved the problem. Pay attention to these abnormalities while driving, and regular AC system cleaning can significantly reduce failure rates. I recommend against DIY attempts - safety first.
We have an old family car that we usually use to pick up and drop off our kids at school, and the most annoying issue is when the air conditioning malfunctions. When the expansion valve fails, the cold air from the vents comes out very slowly, and even after driving for a while, it doesn't get cool enough. There's also a strange noise. My husband taught me a simple check: wait until the car cools down a bit, then feel the temperature of the pipes. If there's no significant difference between the high and low temperatures, it's likely the valve is broken. It's important to go to a proper repair shop promptly to have a technician check the pressure, so you don't delay and end up with a stuffy, hot car that affects your health. The cost isn't high, and the improvement after repair is immediate.
