What to Do If You Forget to Turn Off the Air Conditioner After the Car Is Turned Off?

[IanRose]

It is recommended to restart the car and then turn off the air conditioner. Below is relevant information about leaving the air conditioner on after turning off the car: 1. Hazards: Most car owners do not turn off the air conditioner or let it automatically start with the vehicle, which causes the air conditioning system to automatically activate every time the ignition switch is turned on. The consequence is an immediate high power load on the vehicle, leading to premature engine wear over time, as well as battery drain. Similarly, turning off the engine before turning off the air conditioner is also harmful to the engine. 2. The correct habit should be: Before reaching the destination each time, first turn off the A/C button and let the cold air blow for a few minutes. Use natural wind to eliminate the temperature difference inside and outside the air conditioning ducts to ensure the internal dryness of the air conditioning system and reduce bacterial growth.

[Ariel]

I did the same thing last month! Leaving the AC on after turning off the engine isn't really a big deal. The vehicle's power-off protection design will kick in, automatically cutting off power to the AC within minutes after locking the car. However, doing this frequently can quietly drain the battery, especially in older cars with weaker batteries. Once, my battery was completely dead after just three days of not driving. If you realize you forgot to turn off the AC, restarting the engine and then turning it off is the safest approach. Developing a habit of turning off the AC before shutting down the engine not only protects the battery but also saves some fuel, since the AC compressor doesn't work after the engine stops—just blowing air still consumes quite a bit of electricity.

[SanDaniel]

Oh, I often get lazy about this too! Actually, after the car is turned off, even if the AC switch is still lit, the compressor has already stopped. The main power drain comes from the blower fan. I specifically asked a mechanic about it, and he said modern cars have a delayed power-off function, which at most drains the battery for about an hour. But be careful not to repeatedly do this to an old battery—a friend of mine once had to call for roadside assistance because of it. Now, I’ve made turning off the AC and removing the key a fixed routine, and setting a reminder on my phone for the car charger is also a good idea. If your battery is over three years old, it’s best to check its health.

[LucasDella]

Last time I was in a hurry to get out of the car with my child and forgot to turn it off, but the next day I found it didn't affect starting at all. Actually, when the vehicle is turned off, the air conditioning compressor's clutch disengages, and only the ventilation system uses power. But an old car battery might not last overnight, especially in winter which is more dangerous. I recommend installing a charger with voltage display, and just take a glance at the voltage when getting out of the car. If it's below 12V, it indicates a power leakage. Modification shops can also enable hidden features to set automatic power-off when locking the car. For beginners who can't remember, stick an air conditioning sticker near the keyhole to remind themselves.