Why does the car air conditioner not cool at idle but cools when accelerating?
3 Answers
Reasons why the car air conditioner does not cool at idle but cools when accelerating: 1. Damaged expansion valve: This prevents the formation of high pressure in the system before the expansion valve, causing the high-pressure refrigerant to fail to reach 150Kpa, which results in the evaporator after the expansion valve not cooling down, leading to the air conditioner not cooling. 2. Internal wear of the air conditioner compressor: This causes the pressure between the air conditioner compressor and the expansion valve to not reach 150Kpa~200Kpa, preventing the refrigerant in the system from circulating normally, resulting in the air conditioner not cooling. 3. Idle speed is too low: The car's computer determines that turning on the air conditioner at this time may cause the engine to stall.
When the car's air conditioning is not cool at idle but becomes cool when accelerating, I've encountered this issue several times. Generally, it's due to insufficient rotation speed of the air conditioning compressor caused by low engine RPM. At idle, the engine runs slowly, and the compressor doesn't provide enough cooling capacity, resulting in warm air from the AC. When you accelerate, the engine speed increases, the compressor spins faster, and the cooling effect immediately recovers. Common causes include the condenser fan not working or not spinning fast enough—the fan should dissipate heat at idle but fails to operate, causing the condenser to overheat and affecting the entire system. Another issue could be with the compressor's clutch; if it doesn't engage firmly at low RPM, cooling becomes unstable. Additionally, the AC belt might be slightly loose, slipping at idle but working normally when accelerating. You can manually check if it's tight. Insufficient refrigerant or leaks can also cause this phenomenon, requiring a pressure gauge check for confirmation. For safety, I found that it's best not to delay fixing this issue as it can affect driving comfort. It's advisable to have it checked at a professional shop—the cost isn't high. During regular maintenance, remember to clean the condenser and ensure proper ventilation to prevent such failures.
I've been driving an old car for over a decade, so I'm all too familiar with this AC issue. When it's cool at acceleration but not at idle, it's most likely a stuck cooling fan. At low speeds, the fan should be running at full speed but isn't moving, so the heat can't dissipate, and the AC won't cool. When you accelerate, the fan speed increases, and the airflow makes it cooler. It could also be a faulty electromagnetic clutch in the compressor, which doesn't engage properly at low RPM, causing intermittent cooling. Last time I had this problem, I popped the hood myself to check if the fan's wiring connection was loose, then checked the AC lines for refrigerant leaks—if the pipes feel icy but the vents aren't cold, there's a leak in the system. Of course, a loose engine belt could also be the culprit, as it might not drive the compressor properly at idle. Experience tells me it's best to tackle small issues early—don't wait until the heat hits to regret it. Just find a trusted mechanic to replace the faulty parts; DIY fixes might make things worse. I recommend regular cleaning of the radiator and AC filter to keep the system running smoothly.
