What are the effects of idling a car with the air conditioning on for a long time?
3 Answers
Whether it's cold air or warm air, prolonged use will have certain effects on the engine. When using cold air in summer, the engine control unit increases the engine speed by about 100 RPM. This increases the engine's air intake, leading to more fuel injection and a richer air-fuel mixture. The engine computer uses this method to enhance engine stability. However, a richer mixture can result in incomplete combustion of gasoline, and prolonged idling with the air conditioning on can lead to increased carbon deposits, making the engine less fuel-efficient. Additionally, when the air conditioning is on, the engine works to reduce the heat from the air conditioning condenser, causing the cooling fan to run continuously. If there are issues with the cooling or heat dissipation systems, it can lead to elevated engine coolant temperatures, which may damage the engine. If the vehicle is in a poorly ventilated area or a garage, prolonged idling with the air conditioning on can also increase the risk of carbon monoxide poisoning for occupants. In winter, warm air is generated by the blower circulating air over the heater core. The engine's normal operating temperature is 85°C, and it can only function properly once this temperature is reached. If the warm air is used continuously, the heater core keeps dissipating heat, forcing the engine to increase its speed slightly to maintain the required coolant temperature. This results in higher fuel consumption, and prolonged idling with the warm air on also increases fuel usage and carbon deposits. Whether using cold or warm air, prolonged idling will increase fuel consumption and contribute to engine carbon buildup.
I have personal experience with leaving a car idling with the AC on for extended periods. Last summer, while waiting for friends at the beach, I kept the AC running with the engine idling for over an hour. That same day, I noticed a significant spike in fuel consumption. Later, when I took the car for servicing, the mechanic pointed out severe carbon buildup in the engine. He explained that at idle, the engine runs at low RPMs, and turning on the AC puts additional load on the compressor, which consumes power. This drastically increases engine load, leading to incomplete combustion and accelerated carbon deposits, as well as faster wear on components. The battery can also suffer from excessive discharge, especially in older models, making it harder to start the car if the battery is weak. Moreover, increased emissions harm the environment. Now, if I have to wait for a long time, I either turn off the engine and take a break or get out and walk around to avoid unnecessary strain on the car and costly repairs.
Often driving my family to go shopping on weekends, I idle the car with the AC on while waiting for them to buy things. It feels comfortable, but the cost is significant. The fuel gauge visibly drops—idling itself consumes more fuel, and with the added load from the AC compressor, fuel consumption is several times higher than during normal driving. Additionally, the inefficient combustion accelerates carbon buildup, which over time affects engine performance and even shortens its lifespan. The battery also suffers, especially in the summer heat, increasing the risk of over-discharge. Not to mention the increased pollution—more exhaust emissions negatively impact air quality. My advice: if you're only waiting a few minutes, it's fine, but if it's over fifteen minutes, it's better to turn off the engine—safer and more economical.
