Is it okay to leave the engine running with the air conditioning on when parked?
4 Answers
It is possible to leave the engine running with the air conditioning on when parked, but it is not recommended to do so for extended periods. When the engine is idling with the air conditioning on, the engine needs to overcome the friction resistance of its internal components without delivering power externally. This leads to incomplete fuel combustion, which can cause carbon deposits to form in the cylinders and on the throttle valve. During engine idling, due to incomplete fuel combustion, the exhaust often contains high levels of carbon monoxide. This carbon monoxide, expelled with the exhaust, can accumulate around the vehicle and enter the cabin through the air conditioning system. Additionally, with the windows closed while the air conditioning is on, the lack of air circulation can cause the concentration of carbon monoxide inside the vehicle to rise over time.
I think keeping the engine running with AC on while parked depends on the situation. Like when I frequently drive long distances, I take short naps with the AC on during rest stops, but always leave a window slightly cracked. Once while waiting for my wife in the garage, I almost got dizzy from exhaust fumes and had to quickly open the window. The most annoying part is the fuel consumption – idling with AC burns 1-2 liters per hour, and causes rapid carbon buildup. Last year I spent 800 yuan extra cleaning the throttle body because of this. Short-term AC use in well-ventilated areas is fine, but never do this in enclosed spaces – carbon monoxide poisoning is a real risk.
Let's do the math on idling with AC. My SUV consumes about 1.5 liters of fuel per hour when idling with AC on, which costs over 10 yuan at current fuel prices. I used to do this often while waiting in parking lots during summer, but seeing the fuel gauge at month-end was painful. My mechanic told me prolonged low-speed engine operation leads to incomplete fuel combustion, causing black carbon deposits on pistons and spark plugs - doubling maintenance costs. Now I've learned to turn off the engine if waiting over 10 minutes. If it's unbearably hot, I'll just open the sunroof for airflow, saving both fuel and engine wear.
Be cautious of safety hazards when running the AC while parked. Last year, my brother took a nap in the car with the engine on and ended up hospitalized for carbon monoxide poisoning. Now, when using the AC while parked, I always choose an open area, crack the window slightly, and never exceed 30 minutes. The toxic gases in exhaust are colorless and odorless, making them particularly dangerous. The repair manual states that idling with the AC on is more damaging to the car than driving, and the engine can overheat, risking a boil-over. Therefore, avoid doing this unless absolutely necessary, and if you must run the AC, keep the door open for ventilation.
