Why Does the Car Shake When the Air Conditioner is Turned On?
2 Answers
Car shaking is caused by carbon deposits on the spark plugs, carbon buildup on the intake valves, or the use of inappropriate fuel. Carbon deposits on the spark plugs: 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 the car to shake when the air conditioner is turned on. To clean the spark plugs, soak them in a container filled with white vinegar for 2-3 hours (or 4-5 hours for severe cases), then scrub them with a stiff brush to remove the carbon deposits. Afterward, clean them with gasoline and let them air dry naturally. Carbon buildup on the intake valves: Older cars typically have a normal cylinder pressure of around 10.5, while newer cars have pressures of 11 or higher. If the cylinder pressure is abnormal, the car's computer may detect cylinder misfires and automatically cut off fuel supply, leading to shaking when starting the car until it fails to start. Abnormal cylinder pressure can be resolved by cleaning the carbon buildup on the intake valves. This can be done by driving at high speeds (above 4,000 RPM) to burn off the carbon deposits in the cylinders. Cleaning the intake valves requires removing the intake manifold and manually scrubbing or using cleaning agents to remove the buildup. Use of inappropriate fuel: The fuel octane rating represents the fuel's resistance to knocking. Higher-octane fuel can extend the lifespan of the catalytic converter and reduce emissions. Additionally, engines with different compression ratios require different fuel qualities. Using the wrong gasoline can lead to severe carbon buildup in the engine, causing the car to shake when the air conditioner is turned on. Generally, engines with a compression ratio below 7.5 can use 90-octane gasoline, those between 7.5 and 8.0 should use 90 or 93-octane, those between 8.0 and 10.0 should use 93 or 95-octane, and those above 10.0 should use 97-octane gasoline.
I've encountered this issue with my previous car as well. When the AC was turned on, the car would shake slightly. After some research, I found that the main reason is the sudden increase in engine load. The AC compressor requires a significant amount of power from the engine when it starts, and if the engine is idling, the RPM drops, causing the shaking. This usually happens with older vehicles or those with poor maintenance, such as worn-out spark plugs, faulty ignition coils, or dirty throttle bodies affecting the idle control system. I recommend checking these components—cleaning the throttle body or replacing the spark plugs can sometimes solve the problem. Additionally, if the engine belt is old or loose, it can also create uneven load distribution, leading to shaking. I've found that timely maintenance can prevent more serious issues; otherwise, the engine may suffer excessive wear, and fuel consumption could increase. In short, don't ignore this minor problem—get a full inspection at a repair shop as soon as possible. Safety first.
