Is it okay to keep the air conditioning on without starting the car?
4 Answers
It is possible to turn on the air conditioning without starting the car, but it can cause damage to the vehicle. Below are the potential consequences and reasons: 1. If the air conditioning is left on for an extended period without starting the car, the car battery will be drained. In mild cases, the car may fail to start, while in severe cases, the battery may remain in a chronically undercharged state. This is because, without the engine running, the air conditioning compressor does not work, and the blower fan (which circulates natural air) is powered by the battery. (This applies only to traditional fuel-powered vehicles; electric vehicles do not experience this issue.) 2. Failing to turn off the air conditioning after shutting off the engine can easily damage the engine. The impact on the car is significant because modern vehicles have interlock mechanisms that automatically cut off most auxiliary circuits when the engine is off, including the air conditioning. As a result, when the car is started again, the sudden load from the air conditioning can place excessive strain on the engine. 3. It is not recommended to keep the air conditioning on for long periods while the car is idle. Running the air conditioning for too long while the engine is idling can lead to carbon buildup in the engine and damage the vehicle.
Leaving the car running without starting the engine to use the air conditioning is really not a good idea, especially for traditional fuel-powered vehicles. If the engine isn't running, the compressor can't operate, and the air conditioning simply can't produce cold air—at best, you'll get some natural airflow. But even just using the fan consumes a lot of electricity, relying entirely on the battery. The limited power in the battery can't handle this kind of usage for long. Once, while waiting for someone outside, I thought I'd just turn on the air conditioning and listen to music for a while, but the battery warning light came on in less than half an hour, and I almost had to call a tow truck. Moreover, prolonged use of electricity like this significantly accelerates battery aging. Replacing a battery costs several hundred yuan, which really isn't worth it. Now that summer is here, if you want to stay cool in the car for a long time, it's better to either start the engine or find a shaded spot and open the windows for ventilation—much more practical.
Let's talk about being a new energy vehicle owner: Pure electric vehicles can indeed run the air conditioning without starting the engine, as they directly use the power from the traction battery. However, the real-world experience isn't perfect. The air conditioning consumes a significant amount of power when cooling—I've tested it and found it can drain about 30 km of range per hour. An even bigger issue is with the 12V auxiliary battery. The air conditioning control system actually relies on the 12V battery for power. If the traction battery doesn't recharge the auxiliary battery in time (for example, when not connected to a charger), the auxiliary battery can easily run low. Just last week, I encountered a system alert for a low-voltage fault, and the diagnosis revealed that the auxiliary battery had been deeply discharged. So, while it's okay to use the air conditioning briefly in emergencies, for prolonged use, it's safer to keep the vehicle plugged into a charging station or activate the vehicle ready mode.
This practice directly harms the battery. Car batteries are primarily for starting the engine and have limited capacity. Running the air conditioner at the lowest fan speed for one hour can drain about 10% of the battery's charge, and higher speeds will deplete it even faster. Repeated deep discharges can lead to sulfation of the battery plates, causing a permanent reduction in capacity. I've seen cases where owners napped in their cars with the air conditioner on for three hours, ending up unable to even roll up the windows. Tow truck drivers mention receiving five or six such rescue calls every month. Mechanics advise: if you really need to use electrical devices for a short time, it's best to keep the engine running. Newer cars come with intelligent power management systems that automatically cut off electrical devices when the battery voltage is low, but older vehicles lack this feature, so extra caution is needed.
