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Is it dangerous to leave cars air conditioning on while car is off?

My mom says if you leave your cars air conditioning on when you turn the car off, so it automatically is on when you turn your car on, that it hurts the engine. Is that true or is she full of BS? It sounds like complete BS to me.

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33 Responses to “Is it dangerous to leave cars air conditioning on while car is off?”

  1. Ashley said :

    no its not true

  2. Jen said :


  3. indyanajoana said :

    I am not sure about the engine, but you can run your battery down.

  4. ACE said :

    Absolutely untrue.

  5. Ashton S said :

    it would probably kill your battery and it might damage your car if you left it on for a while

  6. ufos420 said :

    I could say that I doubt it, but I don’t know much about cars. Don’t think they’d sell stuff that would kill on normal usage.

  7. ziko said :

    Well it mainly depends on car. But in most cases it really damages car but not engine. It damages accumulator. So listen your mom. 🙂

  8. tilliam75 said :

    not really but i wouldn’t do it because it can cause energy loss in your car

  9. Dan H said :

    She’s full of it. It makes no difference whether the air conditioner is on or off when you start your car.

  10. dlsjbk2125 said :

    My dad tells me the same thing. I think it is true because when I forget to turn it off my car doesn’t start as well. It is always best to turn it off.

  11. i_love_my_dinosaur89 said :

    its actually true. my dad told me the same thing and still gets onto me when he gets in my truck and its on. and supposedly no matter how low or high you have the a/c on it still uses the same amout of gas…so i keep mine on freezing.. but i dont know..

  12. jhurd67 said :

    its a lot safer than leaving windows down … will not harm car at all

  13. Steve K said :

    idk… but I think my fam and I do it!…
    Good Luck!
    may God be with u all ur life!

  14. Cribber said :

    No. In older cars, it can cause problems with the A/C compressor. In newer cars, the compressor doesn’t come on right away anyway. However, it wont’ hurt the car’s engine regardless of the age of the car.

  15. I Love Luisa Ferdinand said :

    It can actually cause wear and tear more easily by doing that. When you turn on the engine, if your A/C is on, it adds an unecessary amount of extra stress to your engine. A/C’s run directly through your engine’s timing belt and having it on during ignition can be detrimental to your engine’s life. It’s not that big a deal, but there is truth in the theory.

  16. no2censors said :

    it takes more electricity to turn over the engine, but as long as the battery is fine, no problem. she is not full of bull though as it is harder to start because the engine will crank slower. mother knows best in a way but it is no big deal either way.

  17. Triana said :

    not true what your mom said

  18. xokalixo said :

    If the car is off..the air conditioning wouldn’t be on..
    cuz the car needs to be on in order for it to work..
    i am confused by your question.

  19. smexy said :

    no it just wastes battery but not really so your good.

  20. oklatom said :

    Doesn’t hurt a thing. When the switch of off, so is the A/C. When the key is in the start position, none of the accessories, including A/C work. Once it’s up and running and you put the switch in the run position, having the A/C on won’t hurt anything.

  21. JL2 said :

    Wow! You’re mom is fueling the whole “Women and cars don’t mix” stereotype.

  22. Mountain!! said :

    Not true about the engine, but it may hurt the AC. I had a Jeep Cherokee and the manual said to turn off the AC prior to turning off the engine. Not sure why, but after I repeatedly faild to follow the instruction, I had to have work done on it………

  23. James said :

    it shouldnt matter because untill the car gets up to speed the compressor doesnt kick in any ways so its pretty much bs and you should have no problems

  24. kim m said :

    i know it can drain your battery.

  25. Mustanger said :

    No. It isn’t dangerous. When you turn the key to “start” all electrical circuits which are wired through the ignition switch are disconnected, except those which are used for starting the car. When the engine starts and you release the key, from the start position, then all the circuits are again connected. I know a lot of people, most of who don’t know the starter from the distributor, who insist that the AC needs to be switched off before starting the car. I don’t switch it off and never have had a bit of trouble, with either the engine or the AC on any of my cars.

  26. John B said :

    This is true. The AC takes about 10% of your engine’s power when turned on so, when you start it. The starter has to work a little harder to turn and start the engine . The AC unit is a compressor under pressure at all times, so it takes more power to turn. You Mom is a good Mom and you should listen to her and she knows a little more than you think.

  27. Travis C said :

    The AC compressor uses battery power on start-up if you leave it on. It could lower your cold cranking amps over time.

  28. George A said :

    You can leave the selector on AC after you shut the ignition off. I leave the selector on AC (heat/defroster if in winter) and it has not damaged my vehicle. (I bought it with 15K miles in 1995 & it has over 137K now) The AC will not work with just the key on if that is your uestion- all you will do in that case is run the battery down.
    I have had a friend have the fan switch go bad & if he didn’t turn the fan to off, it would allow the battery to drain where he had to jump his car.

  29. Firebird said :

    Wow! out of 23 answers, you had one person who knows how a car works. That’s Mustanger.

    PLEASE, in the future, opens your eyes and look at things. Be inquisitive. If you want to really know the answer to this, would have killed you to open you eye and look at the a/c compressor during starting? I don’t think so.

    And for the apparently huge crowd who thinks leaving the a/c on runs the battery down, I just have this to say: “Y’all been on earth long?”

  30. alcusswhen said :

    I will not say your mom is full of anything. But I will tell you this
    the a/c should be left on. It does not come on untill after the engine is running. So it doesn’t matter where the switch is
    on or off. Ask you mom this! Why would the auto maker go to all the trouble to cut the a/c out of the system until the engine is running, if they wanted you to have to turn it off and on all the time? Just leave it on and don’t worry about it.

  31. mrbungle650 said :

    it is bs.

    the compressor doesnt actually engage until the clutch in the compressor has been activated. until then it is free spinning…when your motors is free spining…so no wear on the starter. or on the motor.

    it is completely fine to do…

    one thing you dont wanna do is leave your a/c on “max ac” the whole time..because your a/c is recirculating only the air inside the car…which will cause your evaporator to freeze and can actually crack it. any manufacturer will tell you only to use max a/c to cool off then to switch to the level right before…i know this is kinda off topic but figured id let you know.

    so yeah..what your doing is fine…dont worry bout it.

  32. tomtom said :

    The belt that most ac’s operate from are turning whether ac is on or not. so no.

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