Why is there noise under the hood when the air conditioning is turned on?

[SanJoseph]

Here are the specific reasons for noise under the hood when the air conditioning is turned on: 1. Dirty or stuck throttle valve: After the air conditioning is activated, the compressor may also start working, and since the compressor is driven by the engine, turning on the air conditioning increases the engine load. This means the engine needs to increase the throttle opening to allow more air intake. When the throttle valve has carbon deposits or is stuck, it can cause engine vibration and produce abnormal noises. This becomes more noticeable after the air conditioning is turned on. 2. Abnormal noise from the air conditioning pump: There are generally two main causes for abnormal noise from the air conditioning pump—the electromagnetic clutch and the bearings inside the air conditioning pump. Noise from the electromagnetic clutch is mainly caused by wear, leading to increased gaps, while noise from the air conditioning pump bearings is usually due to a lack of lubrication. If these issues are not addressed promptly, they can lead to the air conditioning pump burning out and failing to perform cooling work. 3. Improper tension of the compressor drive belt: If the drive belt is too loose, the electromagnetic clutch is prone to slipping; if the drive belt is too tight, the load on the electromagnetic clutch increases. When the drive belt tension is incorrect, it can cause abnormal noises in mild cases and damage the air conditioning compressor in severe cases.

[BrantleyLee]

Engine hood noise when the air conditioning is on is quite common. My previous car used to buzz and vibrate as soon as the AC was turned on. Later, during repairs, it was found that the AC compressor belt was loose or worn out. Over time, belts can wear out and become loose, causing a high-pitched squealing sound when rotating. The fan spinning faster for cooling can also produce a whooshing noise, especially in hot summer when higher speeds might cause resonance. Additionally, a faulty bearing inside the compressor can result in a clicking or screeching sound, while poor refrigerant flow might produce a water-like gurgling noise. I suggest first identifying the type of noise. If it's a belt issue, you can check the tension yourself and replace it if needed. For fan blades stuck with debris, simply clean off the dust. If you're really concerned, take it to a professional shop for a check-up to avoid costly compressor replacements later. Regular maintenance of belts and fans can reduce such issues, ensuring a quieter ride in summer and a better mood overall.

[Gomez]

Dealing with abnormal noises from the vehicle's air conditioning is a common issue I encounter. The noise under the hood when the AC is on is often caused by the compressor starting up: the normal clicking sound from clutch engagement is fine, but a sharp squealing noise indicates bearing wear or improper belt tension. The high-speed rotation of the fan for cooling can produce wind noise, and if the blades are deformed or dirty, it can worsen friction and cause abnormal sounds. Insufficient compressor oil or refrigerant leakage can also lead to unusual flow noises. I use a stethoscope to locate the source of the noise—adjusting the tensioner for belt issues is an inexpensive fix, while bearing failure requires replacing the entire compressor at a higher cost. I advise drivers to clearly identify the noise location when the AC is on and address it promptly to prevent poor cooling and engine overheating. Safety comes first—don't take it lightly. Inspection costs are low, and early repairs save money and hassle.