What Causes the Low-Pressure Pipe of a Car's Air Conditioning to Freeze?
4 Answers
Reasons for the low-pressure pipe of a car's air conditioning freezing: 1. Faulty expansion valve: The low-pressure pipe of a car's air conditioning may freeze largely due to a faulty expansion valve, which fails to sense the real-time temperature of the low-pressure pipe. If the temperature is too low, the low-pressure pipe will inevitably freeze (the opening of the expansion valve cannot be adjusted lower). However, this issue is generally irreparable and requires replacing the expansion valve with a new one. 2. Failed evaporator temperature sensor: It could also be due to a failed evaporator temperature sensor. This component is designed 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 conditioning will stop operating to prevent frost or ice formation. Therefore, when the evaporator temperature sensor fails, it naturally cannot detect the corresponding temperature data, leading to the low-pressure pipe freezing. In this case, a new sensor needs to be installed.
I've been driving for nearly twenty years and have seen many cases of low-pressure AC lines freezing up. The most common cause is insufficient refrigerant, where the system pressure drops too low, causing the evaporator surface temperature to decrease too rapidly and moisture in the air to freeze directly on it. Another possibility is a faulty temperature control sensor, where the compressor keeps running non-stop without shutting off, allowing low temperatures to accumulate continuously. Expansion valve blockage or desiccant failure may also restrict refrigerant flow and exacerbate cooling. Once on the highway, my AC suddenly stopped cooling, and upon inspection, I found the line frozen solid. I immediately turned off the AC, waited about ten minutes for the ice to melt, and then continued driving. I recommend drivers regularly check refrigerant levels, avoid blasting the AC in cold mode when the engine is overheating, and pay extra attention to the cabin air filter during maintenance to prevent such issues and ensure driving safety. After all, freezing can reduce AC efficiency and even damage compressor components.
As an ordinary car owner, I just experienced the annoyance of low-pressure pipe icing. The more I turned on the AC, the less cold air came out, and later when I got out of the car, I felt the pipe frozen rock solid. After researching and discussing with friends, I learned it was due to an imbalance in the refrigeration system—like refrigerant leakage causing a significant drop, leading to rapid pressure loss and abnormally low pipe temperature that attracted moisture and froze. Or, the evaporator fan might have failed, causing insufficient heat dissipation, making the compressor work non-stop and accumulating excessive cooling. That time, I casually added some refrigerant, which didn’t help, and eventually had to visit a repair shop. The mechanic suggested checking components like the thermostat and expansion valve. Normally, while driving, avoid setting the temperature too low for too long, and during maintenance, inspect the pipes for aging or cracks to prevent more trouble and save time and effort.
I'm a car enthusiast and have done in-depth research on air conditioning icing issues. The root cause of icing on the low-pressure pipe is abnormally low system pressure leading to a sudden temperature drop, such as insufficient refrigerant causing excessive cooling of the evaporator, or blocked expansion valves restricting refrigerant flow. Additionally, when the desiccant fails and its moisture absorption capacity weakens, water condensation accelerates frost formation. I've tried self-inspection before but recommend avoiding DIY to prevent equipment damage—professional diagnostics are needed to identify the root cause. For prevention, checking the refrigeration system pressure during seasonal transitions can help detect potential issues early, and simple maintenance can extend the air conditioning's lifespan for smoother operation.
