Why does the Audi Q5L engine make loud noise when starting with AC on?
2 Answers
Audi Q5L may produce brief noise when initially turning on the AC, which is normal. This sound occurs when compressed refrigerant flows through the throttle valve. Engine abnormal noise: Abnormal engine noises most likely originate from the engine compartment. Most people identify it as engine compartment noise based on the sound source, typically manifesting as metallic screeching or whistling noises. When engine abnormal noise occurs, prompt repair is necessary to prevent further damage. AC compressor abnormal noise: Poor AC heat dissipation or blocked pipelines can cause compressor noise. When lacking refrigerant, insufficient lubrication of internal compressor pistons working under high refrigerant pressure may produce metal friction sounds.
I recently encountered a similar situation with my Audi Q5L. When starting the engine cold and turning on the AC, the engine noise does become noticeably louder. Right after ignition, the engine is still in a cold state, and the AC compressor suddenly kicks in at full cooling capacity—it's like asking someone to do heavy lifting right after waking up, which is obviously tough. At this point, the cooling fan revs up to maximum speed, producing a whooshing sound, while the belt tensioner bears a heavier load. Combined with the turbo's whistling noise, the whole car sounds like a symphony. Usually, the noise diminishes significantly once the engine warms up. However, if the loud noise persists for a long time and is accompanied by metallic grinding sounds, it's time to check the compressor bearings—older cars are particularly prone to this issue.
