What Causes Car Vibration When the Air Conditioner is On?
3 Answers
Here are the reasons for car vibration when driving: 1. Spark plugs with carbon deposits: After a period of use, spark plugs can accumulate carbon deposits. If not cleaned in time, this can reduce the engine's torque output, causing vibration when the air conditioner is on. 2. Abnormal cylinder pressure: Generally, older cars have a normal cylinder pressure of around 10.5, while newer cars have pressures of 11 or more. If the cylinder pressure is abnormal, the car's computer will detect cylinder misfire and automatically cut off fuel supply, leading to vibration when starting the car until it fails to start. 3. Poor fuel quality: The fuel octane number represents the fuel's anti-knock index. Higher-grade fuel can extend the lifespan of the three-way catalytic converter and reduce emissions. Additionally, engines with different compression ratios require different fuel qualities. Using the wrong gasoline can cause severe engine carbon deposits, resulting in car vibration when the air conditioner is on.
I also experienced shaking when driving with the air conditioning on before. That time, the weather was hot, and as soon as I turned on the AC, the car started to buzz and shake. The reason is that when the AC starts, the compressor requires extra power to operate, which directly adds a burden to the engine. If your engine already has carbon buildup or an aging ignition system, such as worn-out spark plugs, it's more likely to shake under unstable conditions. Another possibility is that the rubber mounts of the engine mounts are worn out and can no longer absorb vibrations. If the shaking becomes severe, I suggest you immediately turn off the AC to test. If the shaking stops after turning it off, the issue lies with the AC components; if it continues, check the engine and fuel system. For safety, don't push through it—visit a repair shop as soon as possible for a check-up. Additionally, cleaning the fuel injectors and throttle body can help prevent future issues.
The shaking of a car when the air conditioning is on mainly stems from the sudden increase in engine load caused by the compressor starting up. As I've observed, the compressor requires engine power to operate, and the drop in RPM at idle leads to vibrations. Common factors include ignition system defects such as worn spark plug electrodes or aging coils, which worsen combustion; carbon buildup in the intake manifold disrupting the air-fuel mixture ratio; or cracked engine mount rubber failing to absorb vibrations. Air conditioning system malfunctions like seized compressor bearings or refrigerant leaks increasing resistance can also be contributing factors. A simple self-check method: start the engine and turn on the air conditioning to feel if the RPM fluctuates significantly, or turn off the air conditioning to see if the shaking disappears. Regular maintenance, such as replacing the air filter and checking belt tension, can alleviate the issue, preventing increased fuel consumption and part damage.
