Why does the engine make a buzzing sound when the air conditioning is turned on?

[SanRhett]

When the air conditioning is turned on, the buzzing sound from the engine is a manifestation of the condenser dissipating heat, which is a normal phenomenon. Condenser Heat Dissipation: After the car's air conditioning is activated, the refrigerant circulating in the pipes generates a significant amount of heat. This heat is dissipated through the front-end condenser. However, the condenser alone is often insufficient, so there is usually an electric fan of similar size connected to the condenser to assist in heat dissipation. Precautions for the Condenser: During regular use of the air conditioning, it is important to pay attention to the external cleanliness of the condenser. Over time, debris, fluff, dust, and other particles can clog the condenser's cooling fins, leading to issues such as the air conditioning not cooling effectively after prolonged use.

[McAurora]

When I turn on the AC in my car, the engine makes a humming noise. At first, I thought it was a serious problem, but actually, this is quite common. The first thing to check is whether the AC compressor is running normally. When it's working, it drives the belt to rotate. If the belt is loose or worn out, the noise becomes particularly noticeable. Last time during maintenance, the mechanic had me listen to the sound to determine if it was a compressor or belt issue. A faulty compressor bearing can also cause a humming noise, but that sound tends to be more piercing. Additionally, the cooling fan can cause noise, especially in summer when the fan runs at higher speeds due to the heat, making the sound louder. I think if the noise is unusually loud or accompanied by car vibration, it's best to get it checked immediately. Don't wait until the belt breaks or the compressor seizes up, as the repair costs would be much higher then.

[LaAlexa]

I've studied quite a few cases regarding the causes of engine humming when the AC is on. The key is to identify the source of the sound: the noise near the radiator is normal, caused by the high-speed rotation of the fan. However, persistent humming near the pulley area might indicate belt slippage or excessive compressor load. From my own experience, if the noise lasts only a few seconds when the AC is first turned on and then quiets down, it means the compressor clutch is engaging properly. If the humming persists and gets louder, it's likely due to a faulty belt tensioner or worn internal bearings in the compressor. Additionally, in older car models, deteriorated engine mount bushings can cause resonance noises when the AC is turned on. I recommend regularly checking the belt's condition and replacing it if cracks are found, as this can prevent many issues.

[WalterAnn]

Whenever I hear a buzzing sound when turning on the AC, I know it's time to check several key components. The compressor is the prime suspect - if the belt is too tight or too loose during operation, it will cause abnormal noises. Then there's the radiator fan, sudden increases in RPM can also produce a humming sound, especially noticeable when idling at traffic lights. I recommend first identifying the sound pattern: if it synchronizes with engine RPM, it's likely a belt issue; if it varies with AC cooling intensity, it's compressor-related. For DIY inspection, pop the hood and have a friend toggle the AC while you locate the noise source. A quick fix is applying belt anti-slip spray, but that's just a temporary solution - for permanent repair, you'll need a professional mechanic's diagnosis.