What is the method for checking the condition of an expansion valve?
2 Answers
The method for checking the condition of an expansion valve is: 1. Connect the expansion valve to the high and low pressure ends of the manifold gauge set, with the middle hose connected to the charging valve and inject refrigerant; 2. Place the capillary tube of the expansion valve into a water tank and observe the water temperature in the tank and the pressure on the high-pressure gauge; 3. Operate the high-pressure manual valve to make the high-pressure gauge pointer reach 490 kPa, allowing the refrigerant to discharge from the expansion valve in a gaseous state; 4. If the intersection point of the water temperature and high-pressure gauge value falls between the water temperature and high-pressure curves, it indicates the expansion valve is functioning normally. If it does not fall between the two curves, the expansion valve should be repaired or replaced. Symptoms of a faulty automotive expansion valve include: 1. The low-pressure pipe not feeling cold to the touch; 2. Frost formation on the dryer bottle and condenser; 3. No hissing sound heard at the expansion valve or condenser.
To check the condition of the expansion valve, I usually start with a visual inspection. If I find oil stains or traces of green oil leakage near the valve body, it's likely due to poor sealing or internal leakage. Next, I start the air conditioning system and use an infrared temperature gun to measure the inlet and outlet temperatures of the expansion valve. During normal operation, the outlet temperature should be lower. If the temperature difference is too small or unchanged, the expansion valve may be clogged or have excessive opening. It's also important to check whether the high and low side pressure readings are within a reasonable range. Pressure imbalance is often a sign of expansion valve failure. Last time I checked it myself before summer, I found the valve core stuck, and it returned to normal after cleaning. These steps are simple and suitable for DIY to prevent air conditioning failure, but don't overlook the regular replacement of refrigerant.
