What Causes Car Vibration When Turning on the Air Conditioning?
3 Answers
Opening the air conditioning causes car vibration because: the throttle valve is too dirty, which affects the normal operation of the engine. If the air conditioning is turned on at this time, it will increase the engine idle speed, resulting in car vibration. The functions of car air conditioning are: 1. Using the continuous phase change cycle of refrigerant to achieve cooling effect; 2. Removing dust, odors, smoke, and toxic gases from the air inside the car to freshen the air and humidify the cabin air. The maintenance methods for car air conditioning are: 1. Do not set the temperature too low; 2. Control the direction of the air outlet; 3. Do not use it for too long; 4. Appropriately turn on high air volume; 5. Turn off the air conditioning when driving at low speeds.
The other day I noticed the car would shake as soon as the AC was turned on, so I went for a check-up immediately. The mechanic said the most common reason is the sudden increase in engine load when the AC compressor kicks in—it's like asking someone who's taking a leisurely walk to suddenly carry a heavy load. This is especially noticeable in older cars because the engine mounts have aged and their vibration-dampening effect has weakened. Also, if the RPM is too low, like when idling at a red light with the AC on, the ECU might not have enough time to increase the RPM to compensate for the power loss, causing the car to shudder. Incorrect belt tension can also make the compressor work unevenly, causing vibrations throughout the engine bay. Finally, check the spark plugs and throttle body—if there's too much carbon buildup, the throttle response will lag, making it even harder for the engine to handle the additional load from the AC. It's best to address this issue early before the shaking gets so bad you can't even hold the steering wheel steady.
I've studied the principle behind AC-induced shaking: When the compressor kicks in, it instantly demands 10% of the engine's power – equivalent to suddenly adding two adults to the car. The ECU compensates by increasing RPM when it detects insufficient power. But if the throttle body is carbon-clogged or the MAF sensor provides inaccurate data, the ECU miscalculates and fails to raise RPM adequately, causing body vibration. Older vehicles show this more prominently because hardened engine mounts can no longer absorb vibrations that now transmit directly into the cabin. Also inspect the alternator belt – cracks or excessive looseness can make compressor operation erratic. Brief shaking at startup is normal, but persistent vibration warrants checking these three areas.
