1. Increased Engine Load: When the AC compressor engages, it puts extra strain on the engine by requiring more power to drive it. This increased load can cause the engine's RPM to drop slightly.
2. Idle Air Control (IAC) Valve Adjustment: The IAC valve helps regulate the engine's idle speed by controlling the amount of air that bypasses the throttle body. When the AC is turned on, the IAC valve may need to adjust to maintain a stable idle speed. This adjustment can cause temporary fluctuations in RPM and engine shaking.
3. Compressor Cycling: The AC compressor cycles on and off as needed to maintain the desired cabin temperature. When the compressor turns on, it creates a sudden increase in load on the engine, causing a momentary drop in RPM and a vibration or shaking sensation.
4. Refrigerant Pressure: Low refrigerant levels or a faulty expansion valve can affect the AC system's performance and lead to insufficient cooling. This can cause the AC compressor to work harder, putting more strain on the engine and resulting in RPM drops and engine shaking.
5. Engine Mounts: Worn-out or damaged engine mounts can exacerbate the engine shaking issue when the AC is on. These mounts help absorb vibrations from the engine, and when they are weak or broken, the shaking becomes more pronounced.
It's important to note that a slight drop in RPM and a mild vibration when the AC is turned on are generally normal. However, if the RPM drops significantly or the engine shakes excessively, it's advisable to have the vehicle inspected by a qualified mechanic to identify and address any underlying issues.
