What Causes Engine Vibration When the Air Conditioner is On?
4 Answers
Engine vibration when the air conditioner is on can be attributed to the following reasons: 1. Carbon buildup in the vehicle, especially in the throttle body: As the vehicle accumulates more mileage, carbon deposits can form in various parts, particularly in the throttle body. If the throttle body is excessively dirty, it can obstruct air intake, causing the engine to struggle or barely manage to power the compressor. This results in noticeable engine vibration when the air conditioner is turned on. 2. Engine mount collapse or damage: If the engine mount collapses or becomes damaged, the engine's balance is disrupted. When the air conditioner is activated, the compressor's operation may reach a resonant frequency, leading to increased vibration.
There are several common reasons for engine shaking when the air conditioning is turned on. I've encountered this situation and found that it's mainly caused by a sudden increase in engine load. When the air conditioning compressor starts, it consumes power, and if the engine's power reserve is insufficient, it will shake. Older cars are particularly prone to this because carbon deposits inside the engine affect combustion efficiency, coupled with aging spark plugs causing unstable ignition, making misfires more likely when the AC is on. Another possibility is the deterioration of engine mounts, where the rubber cushions are worn out. This isn't usually noticeable, but the increased vibration when the AC is on makes it obvious. Additionally, if the refrigerant pressure in the air conditioning system is too high, it can make the compressor work harder. It's recommended to check for carbon deposits, replace the spark plugs, and inspect the condition of the engine mounts.
Air conditioning-induced shaking is mostly caused by engine mount issues. When the rubber cushions in the engine mounts age, their vibration-damping performance deteriorates, allowing compressor vibrations to directly transmit into the cabin when the AC is on. Compressor malfunctions can also cause shaking, such as weak electromagnetic clutch engagement or bearing seizure. Some vehicles with slipping belts may exhibit similar symptoms, which can be identified by sound. I've serviced several older cars where replacing the engine mounts eliminated even steering wheel vibrations. To diagnose, check if shaking occurs only with AC on - if the engine idles normally but shakes with AC, it's likely mount-related. If RPM fluctuates significantly after AC activation, it could indicate a dirty throttle body affecting air intake.
Air conditioning shaking is mostly related to engine load management. When the air conditioning is turned on, the compressor consumes about 15% of the power, and the computer will increase the speed to compensate. At this time, if the ignition system cannot keep up, it is easy to shake. Old coils or spark plugs perform poorly under high load. Air leakage in the intake pipe or carbon deposits causing an imbalance in the air-fuel mixture can also make the idle speed unstable. A faulty thermostat causing abnormal water temperature may also trigger shaking. In this case, it is recommended to first read the fault code, then check whether the resistance value of the ignition coil meets the standard, and clean the throttle carbon deposits by the way.
