What Causes Engine Shaking When the AC is On?
4 Answers
Engine shaking when the AC is on can be attributed to the following reasons: 1. Severe Engine Carbon Buildup: The most common cause of shaking is a dirty throttle body or excessive carbon deposits in the fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector can be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making it difficult to start. The solution is to clean the fuel system and check if the idle control valve has carbon buildup, which should be cleaned thoroughly. 2. Unstable Fuel Pressure: Check whether the fuel supply pressure and the intake pressure sensor are functioning properly. If the fuel pump's supply pressure is abnormal or the intake pressure sensor's readings are incorrect or malfunctioning, it can cause the vehicle to shake. The solution is to check the fuel pressure and replace the components if necessary. 3. Aging Engine Components: Vehicle shaking can also be related to aging engine mounts. Engine mounts are essentially the shock absorption system of the engine, responsible for absorbing minor vibrations during engine operation.
When I drove my old car, I encountered the issue of engine shaking when the air conditioning was turned on. The main reason was actually the sudden additional load on the engine. After the air conditioning compressor starts, it requires more power from the engine. If the engine idle was already unstable, the shaking would worsen. In my case, after inspection, it was found that the engine mount rubber had aged and lost its elasticity, making the engine vibration more noticeable when the compressor was working. Additionally, loose or worn belts could cause transmission belt vibrations, and carbon buildup in the combustion chamber could reduce efficiency, making the engine more prone to instability when the air conditioning was on. Neglecting regular maintenance, such as replacing spark plugs or cleaning fuel injectors, can easily exacerbate the problem. It's advisable to promptly visit a professional auto shop to check the condition of the mounts, belts, and compressor to prevent long-term shaking from damaging more components. While driving, pay attention to the tachometer; if the RPM drops significantly after turning on the air conditioning, it may indicate an issue with the idle control system.
Having driven for decades, I've noticed that engine shaking when the AC is on is quite common, mainly because the compressor draws a significant amount of power, causing fluctuations in engine output. If the idle control valve is dirty or malfunctioning and fails to adjust the RPM promptly to compensate for the load, shaking occurs. When the AC system is turned on, the engine has to drive the compressor, which puts more strain on the engine's stability than usual high-load operation. I've also observed that if the vehicle's battery is aging or the alternator has issues, unstable power supply can cause the compressor to work abnormally, leading to engine vibrations. Regular checks for throttle carbon buildup and the idle control motor are essential to prevent minor issues from turning into major failures. If severe shaking occurs while running the AC on the highway, it's best to slow down, pull over, and turn off the AC for inspection—safety first. Developing the habit of letting the engine cool down slightly before turning off the AC in daily driving can help protect the system.
I think the engine shaking when the air conditioning is on is mostly due to the additional load impact from the compressor. When the compressor starts, the engine burden increases. If the belt tension is inappropriate or the bearings are worn, it can cause vibrations when transmitting force. If the idle system, such as the speed controller, malfunctions and cannot adapt to load changes, the engine will shake due to fluctuating RPM. Blocked air conditioning pipes can also worsen the shaking. Regular maintenance can reduce such issues, such as changing the oil periodically and cleaning the intake system to keep the engine running smoothly. Addressing minor shaking promptly can prevent major repairs.
