What Causes Frosting on the Low-Pressure Pipe of a Car's Air Conditioning?
2 Answers
Frosting on the low-pressure pipe of a car's air conditioning can occur under the following circumstances: 1. Normal frosting. When the air conditioner starts running, the condensation temperature and pressure are relatively low, and the capillary tube supplies less refrigerant than normal, causing the evaporation pressure to drop. This leads to frosting on the low-pressure supply pipe. However, this frosting and melting process is brief, typically starting after the compressor runs and completing within 5 minutes, after which the air conditioner operates normally. 2. Refrigerant deficiency. When the air conditioner lacks refrigerant, frosting occurs on the low-pressure supply pipe, which is a typical malfunction. This phenomenon manifests as frosting on the low-pressure pipe from the start of operation, persisting even after the compressor runs for over 10 minutes. For older air conditioners, this may be normal and simply require refrigerant replenishment. If the deficiency occurs within two or three years of use or shortly after installation, it is likely due to a leak in the refrigeration system. 3. Partial blockage in the refrigeration system. Blockages often occur at the filter outlet or capillary tube inlet. The throttling effect caused by the blockage reduces the pressure below the normal operating level, resulting in frosting on the supply pipe.
I've been driving for many years and have encountered the issue of frost forming on the low-pressure AC line quite a few times. This is usually caused by insufficient refrigerant in the AC system or a leak point. When refrigerant is low, the pressure in the low-pressure line drops significantly, causing the temperature to fall below freezing, which leads to frost formation when moisture contacts the pipe. Another common cause is a stuck expansion valve, which is responsible for regulating refrigerant flow. When stuck, too much refrigerant flows through, supercooling the pipe. Low fan speed or dust accumulation on the evaporator surface can also affect airflow and heat dissipation, making frost more likely to form. Frost formation is not a minor issue—it reduces the cooling efficiency of the AC and, if left unaddressed for long, can increase the compressor's workload, potentially leading to component damage and higher fuel consumption. I recommend getting the system checked as soon as frost is noticed, proactively cleaning the evaporator and checking fan operation, maintaining regular maintenance, and paying attention to any unusual AC noises while driving to extend its lifespan and save on repair costs.
