What Causes the Low-Pressure Pipe of a Car Air Conditioner to Freeze?
2 Answers
The low-pressure pipe of a car air conditioner freezes due to either excessive refrigerant or a damaged thermistor. Detailed explanations and solutions are as follows: Excessive refrigerant: When too much refrigerant is added to the system, the resulting high pressure causes the expansion valve to remain wide open, allowing excessive refrigerant flow, which leads to freezing of the low-pressure pipe. External hot water can be poured over the pipe, and a tapping test can be performed on the heating pipes to identify the frozen section by sound. Repeatedly applying hot water can then melt the ice at the affected area. Damaged thermistor: While condensation on the low-pressure pipe is normal, freezing indicates that the air conditioning system should stop operating if the thermistor is functioning properly. A frozen condition suggests thermistor failure. The frozen heater core should be removed and thawed.
I've been driving for over 20 years and have encountered low-pressure pipe freezing issues several times. This usually happens when the refrigerant is insufficient, causing the pressure to drop too low, making the pipes extremely cold and leading to freezing. It could also be due to a clogged or malfunctioning expansion valve that fails to regulate refrigerant flow. When the evaporator gets dirty with dust buildup, preventing proper airflow, the temperature keeps dropping until freezing occurs. Another possibility is a faulty thermostat continuously commanding cooling, or high external humidity causing moisture condensation on the pipes. If not repaired promptly, the entire AC system may fail, and the compressor could get damaged. I recommend developing maintenance habits - have refrigerant levels checked and cooling components cleaned annually. Don't cut corners by going to unreliable shops; professional service is more dependable. Driving safety comes first - if you notice problems, pull over and wait for professional assistance.
