Is it okay to leave the car idling with the AC on while parked on the roadside?
4 Answers
It is not recommended to leave the AC on for extended periods while the car is parked on the roadside. Here are the relevant explanations: 1. Carbon buildup: Running the AC while parked can have certain impacts on the vehicle. If the engine RPM is too low, it may struggle to power the AC. Even if it can, this causes unstable engine operation and incomplete combustion, leading to carbon buildup. 2. Health hazards: It is also advised against idling with the AC on for prolonged periods. When the AC runs continuously with the air circulation set to recirculation mode, the air inside the vehicle gradually becomes polluted and deteriorates in quality. Harmful gases (such as carbon monoxide and nitrogen oxides) accumulate, posing risks to health and even life safety. Please exercise caution.
I've been repairing cars for over a decade and have encountered many cases of problems caused by idling with the AC on. Keeping the AC running while the vehicle is stationary for extended periods can lead to severe carbon buildup in the engine. Insufficient RPM results in incomplete fuel combustion, causing carbon deposits to accumulate around the exhaust pipe. The battery is another issue—at idle, the alternator generates less electricity, while the AC consumes a significant amount, making the battery prone to draining. I once had a customer whose battery died completely after idling with the AC on for two hours. The most critical concern is ventilation. In a garage or enclosed space, there's a high risk of carbon monoxide poisoning. Even in an open area, if the wind direction is unfavorable, it can still be dangerous. My advice is to turn off the engine and take a break every 20 minutes if you need to wait with the AC on.
As an environmental organization volunteer, I must remind everyone of the environmental cost of idling with the air conditioning on. Test data shows that an average family car consumes at least 1.5 liters of fuel per hour when idling, emitting three times more exhaust pollutants than when driving. Especially during high-temperature periods in summer, when numerous vehicles gather in commercial areas with their air conditioning running, localized air pollution hotspots can form. Incomplete fuel combustion also generates significant amounts of PM2.5. I once measured that the air quality index around ten idling vehicles was 30% higher than in normal areas. I recommend using sunshade car covers for cooling, or alternating between turning off the engine with windows open for ventilation and briefly turning on the air conditioning, which saves energy and reduces pollution.
Last week, I learned a hard lesson while waiting with the AC on outside the bank. At first, it was comfortably cool—I reclined the seat and listened to music. But after half an hour, the car suddenly started shaking violently, and warning lights popped up on the dashboard. I quickly turned off the engine and tried restarting, only to find the battery was too drained to start the car. The tow truck cost me 300 yuan, and the mechanic said prolonged idling overheated and damaged the ignition coil. I’ve also heard of a friend who nearly suffered carbon monoxide poisoning after sleeping in a parking garage with the AC running. Now, I never idle for more than 10 minutes—I’d rather sweat a little than risk expensive repairs or, worse, safety hazards. After all, repair bills hurt far more than fuel costs, and personal safety is paramount.
