Why is the car air conditioning not cooling at idle but cools when driving?
2 Answers
The reason why the car air conditioning does not cool at idle but cools when driving is: insufficient refrigerant, severely clogged air filter, dirty condenser, faulty air conditioning compressor, damaged expansion valve, or loose air conditioning belt. The solutions are to add refrigerant; check the pipelines, air conditioning pump, condenser, and evaporator in the car air conditioning system for any damage causing refrigerant leakage; inspect the compressor; clean or replace the air filter. Compression process of car air conditioning working principle: The compressor sucks in the low-temperature and low-pressure refrigerant gas at the outlet of the evaporator and compresses it into high-temperature and high-pressure gas, which is then discharged from the compressor. Heat dissipation process of car air conditioning working principle: The high-temperature and high-pressure superheated refrigerant gas enters the condenser. Due to the decrease in pressure and temperature, the refrigerant gas condenses into liquid and releases a large amount of heat. Throttling process of car air conditioning working principle: The higher-temperature and higher-pressure refrigerant liquid passes through the expansion device, causing its volume to increase, and its pressure and temperature drop sharply, discharging from the expansion device in a mist form (fine liquid droplets). Heat absorption process of car air conditioning working principle: The mist-like refrigerant liquid enters the evaporator. Since the boiling point of the refrigerant is much lower than the temperature inside the evaporator, the refrigerant liquid evaporates into gas. During the evaporation process, it absorbs a large amount of surrounding heat, and then the low-temperature and low-pressure refrigerant vapor re-enters the compressor. This working principle process repeats continuously, thereby achieving the purpose of reducing the air temperature around the evaporator.
This issue is commonly encountered by car owners, and I've dealt with many similar cases during repairs. The main reason is that at idle speed, the engine's RPM is low, leading to insufficient driving of the air conditioning compressor. The slower rotation results in poor cooling performance, and the fan may also rotate too slowly, causing inadequate heat dissipation. Once the car starts moving and the engine RPM increases, the compressor's efficiency improves, providing better cooling. Key checks include verifying whether the cooling fan operates properly at idle, ensuring the refrigerant pressure is adequate, and sometimes checking if a clogged air filter affects airflow. It's advisable to avoid prolonged use of the air conditioning at idle. Regularly cleaning the condenser fins to prevent blockages and promptly visiting a professional shop for system testing can prevent minor issues from escalating.
