How Long Can You Run the Air Conditioning After the Car Is Turned Off?
4 Answers
You can run the air conditioning for a short period after the car is turned off. However, there is no cooling function, and prolonged use can easily drain the battery. Therefore, it is not recommended to keep the air conditioning on for extended periods while the engine is off. If you need ventilation, switch to the external circulation mode to allow fresh air to enter the cabin. Additional notes on common misconceptions about car air conditioning usage: 1. Smoking in the car with the air conditioning on: Some people smoke in the car while parked or waiting, which is harmful to health because the closed doors and windows trap the smoke, irritating the eyes and respiratory system. If you must smoke, adjust the air conditioning ventilation control to the "exhaust" position. 2. Always using the internal circulation mode: Some drivers keep the air conditioning in internal circulation mode, which is not ideal. The air conditioning mode should be adjusted based on temperature and environment. Internal circulation can be used but not for long periods. It's best to start with external circulation when turning on the air conditioning and switch to internal circulation after the temperature drops. 3. Setting the air conditioning temperature arbitrarily: Drivers often set the temperature very low for comfort, but prolonged exposure to low temperatures can disrupt the body's endocrine system and cause illness. Setting the temperature below 20°C can lead to various discomforts.
Last time I drove out, it was extremely hot in summer, so I turned off the engine and turned on the air conditioner in the parking lot for more than 20 minutes. The car is an old model from five years ago, the fan sound gradually became quieter, the temperature inside the car rose, and the dashboard showed the battery voltage dropped to 10.8 volts, almost failing to start. I asked a car repair friend, and he said that when the car is turned off and the air conditioner is on, it relies entirely on the battery for power. A regular lead-acid battery has a capacity of about 50Ah, and the air conditioner fan consumes about 5-10 amps. Theoretically, it could last for 5 hours, but due to battery aging and circuit losses, it actually lasts at most half an hour before running out of power. Especially for older cars, the battery performance declines quickly, and it might not even last 15 minutes. During regular maintenance, it's recommended to check if the battery terminals are loose and clean, ensuring the voltage is at least above 12 volts for a safe range. Now, when I park and turn on the air conditioner, I only dare to do it for a short time, within 10 minutes, to avoid trouble and having to call a tow truck, which is really troublesome. Remember to leave a gap in the car window for ventilation to keep the air flowing, which is more reassuring.
I think extra caution is needed regarding safety hazards when running the AC with the engine off. Having driven for ten years, I once had my car parked roadside in winter snow with the engine off and heater running for over half an hour, which drained the battery and nearly left me frozen inside. Normally, a battery can only power the fan for 20 to 30 minutes—newer models with more protective features might last slightly longer, but temperature fluctuations increase risks. Prolonged sealing in the car can lead to oxygen deficiency and dizziness, so it's best to crack a window slightly. Frequent deep discharges from this practice accelerate battery degradation, making the several hundred dollars replacement cost not worth it. My advice is not to prioritize comfort over safety—limit engine-off AC use to under 10 minutes or monitor voltage via a mobile app, shutting it off promptly if below 11.5 volts. Develop habits like turning off headlights and audio systems when parked to reduce load and extend duration, but never take risks that could compromise your drive.
I have studied the principle of running the car's air conditioning with the engine off. When the engine is off, the air conditioning compressor doesn't work, and only the fan consumes power, approximately 50 watts. With a standard battery capacity of 60 ampere-hours, theoretically it could last 12 hours, but in reality, due to losses, it might only last about six hours. The duration depends on the car model and type of air conditioning. For example, manual fans consume less power, but in high-temperature environments, the demand increases, shortening the duration. I tested my car with the engine off and air conditioning on for 25 minutes, and the voltage dropped to a dangerous 11 volts. Generally, it's not recommended to exceed half an hour, as a dead battery can cause inconvenience by preventing the car from starting. It's important to pay attention to battery maintenance and check it regularly while driving.
