What Causes the Low-Pressure Pipe of a Car Air Conditioner to Freeze?

[Rod]

Here are the reasons why the low-pressure pipe of a car air conditioner may freeze: 1. Faulty expansion valve: The freezing of the low-pressure pipe in a car air conditioner is most likely due to a faulty expansion valve, which fails to sense the real-time temperature of the low-pressure pipe. At this time, if the temperature is too low, the low-pressure pipe will inevitably freeze (the opening of the expansion valve cannot be adjusted lower). However, in most cases, this issue cannot be repaired, and a new expansion valve needs to be replaced. 2. Failed evaporator temperature sensor: It is important to know that this component is used to detect the surface temperature of the evaporator and then input the data to the automatic air conditioning control unit. When the temperature drops below 2°C, the air conditioner will stop operating, leading to frost or ice formation. Naturally, if the evaporator temperature sensor fails, it cannot detect the corresponding temperature data, resulting in the freezing of the low-pressure pipe. In this case, a new sensor needs to be replaced.

[VonAngela]

I often encounter this issue at the auto repair shop. Low-pressure pipe icing is mostly caused by insufficient refrigerant or a stuck expansion valve, which leads to the evaporator temperature dropping too low and causing frost. Other possible causes include a clogged air filter reducing airflow, a faulty evaporator temperature sensor sending incorrect signals, or moisture in the AC system causing ice blockages. There have been particularly many such cases recently during summer, mostly due to long-term lack of maintenance. I recommend first testing the system pressure to determine whether it's a refrigerant shortage or an expansion valve issue. Delayed action could even damage the compressor. During inspection, it's best to check the pipe sealing and the dryer bottle as well. Usually, cleaning the filter and replacing the refrigerant can solve the problem, but more complex cases may require replacing the expansion valve.