Skip the auto shop - Our mechanics make house calls

Q: Can running the blowers for the AC with the engine off drain the battery?

asked by on

I have gone out to my car on my 45-min lunch break several other times and used the radio and the AC blower fans to move the air in the car and have not had any issues with a dead/weak battery. Today I went out and used the blowers for about 45-min while I did some work on my laptop. It made the battery so weak that the starter motor would turn but not enough to crank the engine. I left the car sit for a few hours and when I left at the end of the day, it started fine. Will running the AC blowers really draw that much battery power to drain it that much? I've done it before with no issues until today. Any thoughts? Thanks!

My car has 11260 miles.
My car has an automatic transmission.

The problem is although the current draw over 45 minutes might be "low", your battery might be weak, meaning it could have a bad cell and a low reserve capacity. It doesn’t take much to "drain" a weak battery. A confusing thing though is your car is only a year or two old thus making a weak (i.e., "old") battery hypothesis, well, weak. Nevertheless, the thing to do is have your battery load tested (any battery shop will do this for free) to determine its actual condition. If it passes the load test (ask for copy of results so you can see the margin by which it passed), it is possible you have excess current draw in your car’s electrical system. Also consider the possibility that during your most recent break, maybe you inadvertently turned the headlights on which would add to the discharge. Get your battery tested, and if it is OK but the starting difficulty returns, a certified technician from YourMechanic, can diagnose your electrical system.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Can running the blowers for the AC with the engine off drain the battery?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Interior lights do not work - 1987 Jeep Grand Wagoneer

From your description, it sounds like a professional mechanic with great electrical diagnostic skills, like a certified technician from YourMechanic, will need to look at the vehicle, with or without a wiring diagram, to get to the bottom of the...

Q: Car stalling out briefly at 70 MPH

Hello. If there is a problem with the variable valve timeing, VTEC, or with the oil pressure, then the vehicle will definitely act this way. The oil leak needs to be found first. It should not be hard since it...

Q: My air only gets cold while I'm driving. What's going on?

Hi there. One of the most common causes of the symptom you're describing is when you have a bad or failing AC high pressure hose. The high pressure hose is designed to increase and decrease AC pressure during different driving...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.