What Causes the Car AC Not Cooling at Idle but Working Normally While Driving?
3 Answers
Here are the specific reasons why a car's AC does not cool at idle but functions normally while driving: 1. Dirty AC filter: If maintenance has not been performed for a long time, a clogged filter may affect the cooling efficiency of the AC. 2. Dirty condenser: A dirty condenser can also lead to poor cooling performance. The car's AC condenser is located at the front of the vehicle and can be cleaned using a water hose. 3. Insufficient refrigerant: Low refrigerant levels in the AC system's pipelines reduce pressure, resulting in poor cooling. Refill the refrigerant and check for any leaks in the AC piping.
I've seen this situation quite often during car repairs. The AC doesn't cool well at idle but works fine when driving, mainly due to heat dissipation issues. When the car is stationary, the cooling of the AC condenser relies solely on the fan. If the fan speed is insufficient or the AC condenser is clogged with bugs and leaves, the heat can't be expelled, leading to poor cooling performance. When driving, natural airflow helps with cooling, so the AC works better again. Another possibility is an aging or loose compressor belt, which slips at idle, causing the compressor to turn slower. At higher speeds, the belt tightens and the issue resolves. Low refrigerant levels can also affect performance, as the pressure isn't sufficient at idle. My usual approach is to first clean the condenser, then check the belt tension and refrigerant pressure, which generally solves the problem.
Last week my car had the same issue, blowing hot air at red lights and cooling down when moving. The mechanic said the cooling fan was the culprit. If it doesn't spin fast enough or at all at idle, the radiator can't cool down. But when driving, the airflow masks the fan problem. It could also be a clogged expansion valve or slight refrigerant leak causing insufficient system pressure at idle. Another less common reason: a faulty electric fan control module where the temperature sensor gives false readings making the fan lazy. In my case, it was a bad fan resistor - replaced it for 200 yuan and fixed immediately. Suggest checking if the fan spins first before rushing to replace the compressor.
