What are the reasons for frosting on the high-pressure pipe of the Passat B5 air conditioning system?

[DiAaron]

Here are the reasons and solutions for frosting on the high-pressure pipe of the Passat B5 air conditioning system: Expansion valve blockage: The expansion valve of the Passat B5 is located at the high-pressure pipe joint. There is a screw on the high-pressure pipe. After removing it together with the evaporator, the expansion valve is inside the pipe. Clean it and reinstall it. System dirt blockage: Generally, due to dirt blockage at the dryer, a throttling effect occurs. Check the dryer, which should be very cold. Replace the dryer and blow the system with nitrogen. 4-way valve blockage: Check the air conditioning system, add Freon, and check if the 4-way valve is blocked.