Why does the air conditioning not cool at idle but cools when accelerating?
3 Answers
Here are the reasons why the air conditioning does not cool at idle but cools when accelerating: 1. Expansion valve damage: This prevents the formation of high pressure in the system before the expansion valve, causing the high-pressure refrigerant to fail to reach 150Kpa. As a result, the evaporator behind the expansion valve cannot cool down, leading to the air conditioning not cooling. 2. Internal wear of the air conditioning compressor: This results in the pressure between the air conditioning compressor and the expansion valve not reaching 150Kpa~200Kpa, preventing the refrigerant in the system from circulating normally and causing the air conditioning not to cool. The idle speed can be adjusted by changing the throttle opening size, among other methods. Generally, the optimal idle speed is the lowest speed at which the engine does not shake.
I also frequently drive long distances, and it's common for the AC to be weak at idle but cool down immediately when accelerating. Essentially, at idle, the engine's low RPM means the AC compressor can't keep up, resulting in poor cooling performance. When you press the accelerator, the RPM surges, the compressor spins faster, and the cooling effect improves instantly. Possible causes include worn or slipping compressor clutch at low RPM, a loose belt that can't maintain tension, or insufficient cooling due to the condenser fan not spinning fast enough when parked. Driving for long periods in summer heat can be uncomfortable and affect concentration, so it's best to visit a professional shop to inspect the AC system, check refrigerant pressure, and test the fan operation. While you're at it, clean the engine bay to prevent dust buildup and avoid unexpected breakdowns on the road.
I've encountered this issue multiple times on the road: the AC blows warm air at idle but cools down when accelerating. At idle, the engine runs slowly and the compressor struggles to provide cooling, while acceleration brings sufficient power for faster cooling. The main causes could be AC compressor clutch slippage at low speeds or insufficient refrigerant causing pressure fluctuations. Simple self-check: Start the car and listen for abnormal fan noises; if it only gets noisy when accelerating, it indicates a stuck low-speed fan affecting heat dissipation. To avoid compressor damage, spend a little on refrigerant recharge or condenser cleaning. Remember to regularly check belt tension during maintenance, and don't wait until summer when the AC fails to get it fixed.
