Why does the car air conditioner not cool when driving on the highway?
4 Answers
Introduction to the reasons why the car air conditioner does not cool when driving on the highway: 1. Reason one: Lack of refrigerant. Car air conditioners generally need to add refrigerant every 2~3 years. 2. Reason two: Damaged air conditioner flap. The failure of the air conditioner flap motor is relatively rare. The flap motor is usually located in the lower middle part of the instrument panel and serves as the main switch for the air conditioner vents. 3. Reason three: The condenser is too dirty. The purpose of cleaning the radiator and condenser is mainly for heat dissipation. If spring willow catkins and poplar catkins accumulate on the condenser, it can cause phenomena such as excessive engine temperature or poor air conditioning performance. 4. Reason four: Damage to the air conditioner compressor, throttle valve, or expansion valve. Malfunctions in the expansion valve and throttle valve directly lead to poor air conditioning performance. These checks are relatively complicated and require professional repair shops for repairs.
I encountered the same issue with my car on the highway last year, which is actually quite common. The main reason is that at high speeds, the condenser might be clogged—for example, if the front grille is covered with insect remains and dust, the cooling efficiency drops. Additionally, if the refrigerant is insufficient or contaminated, the pressure fluctuates significantly during high-speed cooling, making the cycle inefficient. Another possibility is a loose or worn water pump belt, which can slip at high RPMs, preventing the compressor from functioning. For inspection, you can first check if the condenser is dirty. If that’s not the issue, visit a professional shop to test the refrigerant pressure and the tension of the compressor belt. Don’t delay—driving without AC in summer is unbearable.
As a seasoned long-distance driver, I've found that if the AC isn't cooling well at high speeds, it's mostly due to condenser issues. While the airflow is strong at high speeds, the cooling efficiency drops because the condenser mesh in front of the radiator gets clogged with mosquitoes and dust, preventing heat dissipation. I've also encountered stuck expansion valves where refrigerant flow becomes restricted at high speeds despite working fine at low to medium speeds. A simple solution is to use a high-pressure water jet to clean the condenser surface, being careful not to damage the cooling fins. Additionally, check the AC filter – if it's too dirty, reduced airflow can affect performance. It's recommended to clean the front radiator area every 5,000 kilometers.
It's really annoying when the AC suddenly stops cooling on the highway. Last week I did some troubleshooting myself - first checked the cabin air filter and sure enough, it was clogged with half a centimeter of dust. After replacing it, the airflow from the vents improved significantly. Low refrigerant level is more critical - insufficient pressure can't drive the high-speed circulation. Leaks in the piping system are also common causes, especially when rubber hoses age and crack. Use fluorescent dye to detect leaks. It's best to regularly perform AC system pressure tests and handle leak repairs plus refrigerant recharge together - more cost-effective than fixing them separately. When washing your car, ask the mechanic to rinse the front of the radiator to prevent insect debris buildup.
