Why is there abnormal noise when stepping on the accelerator with the air conditioning on?
3 Answers
1. The abnormal noise is related to engine speed: Most common abnormal noises in the engine depend on the engine speed state. The noise exists during idle or low-speed operation. Possible 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. 2. The abnormal noise is related to load: Many abnormal noises in the engine are clearly related to its load. When a cylinder is cut off, the noise disappears or reduces. Possible causes include: piston knocking; loose connecting rod bearing; piston ring leakage; broken piston pin. 3. The abnormal noise is related to temperature: Noise occurs at low temperatures and decreases or even disappears as the temperature rises. Possible causes include: excessive clearance between the piston and cylinder wall; piston issues due to incorrect depth and width of the main bearing oil groove.
I have experience with the strange noise when stepping on the accelerator after turning on the AC. The main issue is that when the compressor starts, the engine load suddenly increases, causing the belt to slip and produce a squeaking sound. Last time I encountered this, it was because the belt had aged and hardened, making a noise like a mouse squeaking when accelerating with the AC on. Additionally, a worn tensioner pulley bearing can also cause noise, especially in older cars where rubber components tend to degrade. If the belt is loose, the noise is even more noticeable—remember to check the belt’s condition for fine cracks. Another possibility is an issue with the compressor clutch engagement, which produces a distinct rattling sound. These components in the engine bay are all interconnected, so if you hear strange noises, it’s best to first inspect the belt and tensioner pulley. If that doesn’t solve the problem, you may need to replace the parts.
This is a common issue during car repairs. When you turn on the AC and step on the gas, abnormal noises usually stem from these few causes: First, it could be a belt system problem. The compressor starting up doubles the engine load, and if the belt is worn, hardened, or loose, it will definitely slip and make noise. A damaged tensioner pulley bearing can also cause a humming sound during acceleration—I usually remove the wheel and spin it by hand to listen. The compressor itself might also be the culprit; if the clutch plates are worn, they can produce a clicking noise when engaging. Additionally, aged engine mounts can amplify vibration noises. To address this, you need to identify the noise source—whether it’s coming from the belt area or the compressor itself. It’s best to use a stethoscope for precise localization. If the belt needs replacing, replace the entire set and check all the idler pulleys while you’re at it.
