Why does the engine shake severely when the AC is turned on?
2 Answers
The reasons for engine shaking when the AC is turned on are as follows: 1. Incorrect air-fuel mixture ratio: The air-fuel mixture ratio is inaccurately adjusted, which occurs in both open-loop and closed-loop control systems. In vehicles with closed-loop control, the minimum operating temperature of the oxygen sensor is 370 degrees Celsius. If the car has just been started, the temperature in the exhaust pipe may not reach 370 degrees Celsius, causing the oxygen sensor to not function. 2. Low temperature: The temperature inside the engine is insufficient, and both the fuel and lubricating oil are not warm enough. Therefore, more fuel should be injected during cold starts to meet the power requirements. The larger the spark plug gap, the smaller the ignition energy. At low temperatures, fuel atomization is poor, requiring higher ignition energy. Over time, the spark plug gap tends to widen, leading to reduced ignition energy, which affects performance and causes the car to shake. 3. Faulty coolant temperature sensor: The coolant temperature sensor is one of the key inputs for the engine control unit (ECU) to determine engine conditions. If the engine is cold-started at a temperature of -10 degrees Celsius, the ECU will inject fuel based on a 20-degree Celsius condition, resulting in less fuel being injected, which naturally causes shaking.
I drove that old car for several years and encountered a situation where the engine would shake so much that the steering wheel vibrated when the air conditioning was turned on. This is mainly because the compressor consumes engine power when the AC starts. If the engine itself has unstable idling, such as due to aging spark plugs, excessive carbon buildup, or issues with the ignition system, the increased load can easily cause shaking. I remember that time the problem was with the spark plugs, and replacing them made a big difference. Or, a loose or slipping belt could also cause this. Regular maintenance, such as cleaning the throttle body and checking belt tension, can help prevent such issues. Before using the AC in the summer, it's best to visit a repair shop for a check-up, as prolonged shaking can damage the engine. Don’t make the same mistake I did by delaying repairs and ending up spending a lot more on major fixes.
