Why Does the Engine Shake When the Car Air Conditioner is On?
2 Answers
The reasons for engine shaking when the car air conditioner is on are: 1. Spark plug carbon buildup; 2. Throttle valve carbon buildup; 3. Fan deformation or loose screws. The solutions for engine shaking when the car air conditioner is on are: 1. Clean or replace the spark plugs; 2. Clean the throttle valve; 3. Replace the fan. The methods for using the air conditioner are: 1. Turn on the AC switch; 2. Adjust the air vent selector knob—direct the air vent upward when cooling and downward when heating; 3. Adjust the fan speed switch; 4. Adjust the air circulation mode selector knob; 5. Adjust the temperature control knob. The maintenance methods for the air conditioner are: 1. Clean the air vents promptly; 2. Maintain the air conditioner condenser in a timely manner; 3. Clean or replace the air filter element promptly.
I've encountered this issue several times. When the AC is turned on, the engine shakes, mostly because the compressor starting up increases the engine's load, just like a person carrying something and walking unsteadily. This is especially common in older cars with small displacements. Last time I helped my neighbor check his old Jetta, we found two out of four ignition coils were faulty, causing an imbalance in cylinder operation. As soon as the compressor started, the shaking became severe. Another possible reason is the aging or cracking of engine mounts, which are supposed to cushion the engine's vibrations but fail when worn out. There's also a less common reason many people don't think of: an air leak in the intake system. My ten-year-old car had this issue—the air filter box had a crack. Without the AC on, it was fine, but once the AC was turned on, the engine shook like a sieve. I recommend checking the spark plugs and ignition coils first, then inspecting the engine mounts.
