What Causes the Abnormal Noise When Accelerating with Air Conditioning On in a Car?

[LeEmilia]

The relationship between abnormal noise and engine speed: Most common abnormal noises in an engine depend on the engine's speed state. Specific reasons are as follows: 1. The noise only exists at idle or low-speed operation. Causes include: excessive clearance between the piston and cylinder wall; overly tight piston pin or connecting rod bearing assembly; excessive clearance between the tappet and its guide hole; wear on the camshaft profile; sometimes, a loose starter causing pulley noise (noticeable during speed changes). 2. The noise becomes chaotic at a certain speed, with brief sounds emitted during rapid deceleration. Causes include: cracked camshaft timing gear or loose fixing nut; broken crankshaft; loose piston pin bushing; excessive axial clearance of the camshaft or loose bushing. 3. The noise appears during rapid acceleration and persists during high-speed operation. Causes include: loose connecting rod bearing, melted or mismatched bearing shell; loose crankshaft bearing or melted bearing shell; broken piston pin; broken crankshaft.