Can leaving a car idle with the AC running cause the battery to die?

Question

*Before I explain what happened i just want to say that the car’s fuel tank was nearly full*
My friend wanted to go to the mall for a while and I told her that I wanted to wait in the car until she came back. While she was gone, I thought I’d roll the windows down because it was hot in the car but that did nothing- so I decided I’d turn on her car’s AC for a while just until she got back. About 15-20 minutes passed and as she was coming out of the mall, the car battery suddenly died. She got really upset with me and told me that I shouldn’t have used the air conditioning while she was gone and that it caused the car battery to fail. We waited for two hours to leave before someone came and helped us jump start the car. We haven’t spoken for a week, but I’ve been wondering if it was really my fault that the car battery died. I always leave the AC running in my car while I’m waiting waiting for someone and my car battery has never died on me. Was the whole situation really my fault or was my friend’s car battery just faulty in the first place?
I’m sorry if this comes off as ignorant or dumb, I just have very little knowledge about cars. Thank you in advance for your responses!

Answer 1

Most people run the heater-a/c blower on high when the car is really hot, and a blower on high draws significant current. But the alternator of an idling engine should be able to power the blower. Were the headlights on? Anything else on?



Maybe something is wrong with her charging system (alternator)? She should get her alternator checked.



Is there a voltmeter or a battery warning light in her car?

Answer 2

Assuming you started the car and left it idling then yes it is possible to kill the battery. The problem is that the newer SI alternators used by most car makers has a minimum threshold speed that must be reached before they start charging the battery. If you did not speed the engine up beyond that speed then the alternator would not charge the battery and the A/C system is a heavy electrical load because the clutch on the compressor pulls about 10 amps, the blower 6-10 amps and the engine cooling fan as much as 40 amps. At that rate it would not take more than about 30 minutes to drain a good battery and even less time to drain a weak battery. When battery voltage reaches the lower operating threshold of the computer it shuts down to protect the circuitry.

Answer 3

IT is NOT good for the pricey CATALYTIC CONVERTER. ot can OVER HEAT! SO shut the car DOWN and do not allow things to over heat. It can stress out the alternator if the brushes are dirty or worn some. Cars are made NOW to start and run immediately. THis is ALSO to allow aIR TO TRAVGEL OVER THE hot CONVERTER UNDER THE CAR! good luck!.

Answer 4

If the battery did in fact die, it's due to the battery being old and defective or alternately the voltage regulator going bad, not running the A/C. The engine drives the air conditioning compressor, as well as the alternator which keeps the battery charged. Running the fan does draw from the battery, which would drop the voltage, which would trigger the voltage regulator to increase the output from the alternator. The increased load on the alternator would put more drag on the engine, which would cause the car to increase the throttle slightly to maintain idle RPMs.



So no, if the engine was running, the A/C would not cause the battery to die. It would be a bad battery or bad regulator causing that, or there's some piece of information missing such as you didn't actually have the engine running and just the fan was running to drain the battery. Whether you directly caused it or not, your friend is being a dick to not forgive you and not speak to you for so long over what was a simple mistake. She needs to grow up and move on.

Answer 5

It is not your fault, the battery must have been weak.

Answer 6

I am thinking the engine was not running and you just turned the fan on. When the engine is running, the car's battery does not die unless the battery light is on which means the alternator is not charging the battery. You have your story mixed up.

Answer 7

The car was running, charging the battery, and the ac does not draw exceptional current, so the battery was weak, and will fail soon, I bet 'cha. (She may NOT tell you, though).

Answer 8

The battery in a car is only there to start it and operate accessories when the engine isn't running. When the engine is running the alternator delivers more than enough electrical power to operate the electrical systems (incl the air-con) and recharge the battery at the same time. In fact alternators are so efficient that they have to dump the excess electricity by converting it to heat and dissipating it through the regulator.

You don't say but I assume you had the motor running because the a/c only works if the motor is running. If not it was only the blower-fan working. But running the fan only wouldn't drain the battery in 20minutes. A blower fan draws less than 1 Amp so a fully charged car battery should be able to run that fan for several hours.

Answer 9

The AC in a car does not work properly unless the engine is running. Otherwise, if you just turn on the key without starting it, it is just the fan blowing ambient air - not actual air conditioning. And yes, if you do this it will kill the battery. If you had started the engine, not only would you have gotten nice, cool air conditioning but the alternator (being turned by the running engine) would have kept the battery charged. Sure, this burns some gas but with modern engines it would maybe have burned $0.25 worth of gas.



Also, if your friend can't forgive you this minor transgression, she was not your friend in the fist place and you are better off rid of her.