Why Does a Car's Expansion Valve Get Clogged?
2 Answers
If the expansion valve is clogged, it can easily cause the evaporator to freeze when the air conditioning is on for a long time. Once the evaporator freezes, the air conditioning will produce cool air but no airflow. Here are the reasons for a car's expansion valve clogging: 1. Expansion valve clogging. Symptoms include higher temperature at the cold air vents, lower pressure on the high-pressure side, and negative pressure on the low-pressure side. In cases of partial clogging, frost or condensation may appear at the inlet of the expansion valve; in complete clogging, there is no temperature difference between the inlet and outlet. 2. The expansion valve opening being too small or malfunctioning, with symptoms similar to clogging. 3. The expansion valve opening being too large, resulting in higher temperature at the cold air vents and higher pressure on the low-pressure side.
I've seen too many cars with clogged expansion valves at the auto repair shop, mostly due to impurities in the air conditioning lines. The usual culprits are metal shavings from aging pipes that fall off due to driving vibrations, or dust and welding slag accidentally introduced during repairs, which can block the small holes in the expansion valve like a plug. Some cars have a failed receiver-drier, where the desiccant powder inside leaks and clogs the valve. Once the valve is blocked, the refrigerant can't pass through, causing the AC to blow weak or stop working entirely. If you encounter an AC that's not cooling and is frosting up, it's best to check the entire air conditioning line. Simply replacing the expansion valve might only be a temporary fix; you may need to disassemble and clean the lines or replace the receiver tank.
