How Long Can I Leave the AC on While My Engine Is Not Running? | YourMechanic Advice

How Long Can I Leave the AC on While My Engine Is Not Running?

You’ve parked your car, and are sitting inside waiting. Maybe you’re early for work and don’t want to head into the office just yet. Maybe you’re waiting for your spouse to get done in the convenience store. You don’t want to waste gas, so you turn off the engine, but it’s warm, so you leave the blower running. You know this pulls current from the battery, but just how long can you leave the AC on while your engine isn’t running?

Actually, this is a trick question. You cannot run the AC without the engine running. The air conditioner compressor and clutch are operated by the serpentine belt that runs your other accessories (your alternator, for instance). If the engine isn’t running, then the belt isn’t turning. That means your air conditioner’s not actually on. You cannot use the air conditioner if the engine is not running. It’s as simple as that.

What you’re really doing is running the blower motor. As long as there’s a charge in your battery and you’ve got the key set to the on position (some cars will let you run the blower in the ACC position, too), the blower will continue to operate. However, it’s only blowing air from the outside through the cabin, unless you have recirculate mode active. In that case, it’s just recycling the air in the cabin. It does not actually cool the air. Any sensation of coolness is simply because the air is moving, rather than still.


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Joel

29 years of experience
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Joel
29 years of experience
Dodge Dakota - Electric Problems - Phoenix, Arizona
Joel was very knowledgeable, and did what 3 other mechanic's couldn't. He found out short, and now the problem has been resolved. Thank you again Joel for the 5 Star service!
Chevrolet Silverado 1500 Classic - Electric Problems - Peoria, Arizona
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Chevrolet Express 2500 - Electric Problems - Glendale, Arizona
Diego was professional & spent several hours on a Diagnostic...he was unable to isolate & identity the specific Battery drain problem, but did provide helpful evaluation number ranges to help with future eliminations.
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Diego was very professional and explained to me what I need to do so this does not happen again. Very good person I will recommend him highly for future work. He knows what to do and quickly finds the issue to fix.... thank you for having him on your team. Best regards, Kent Robertson

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Mitsubishi Eclipse - Electric Problems - San Antonio, Texas
All I can say he did an awesome job. Was very professional I would recommend him to all my friends and family!
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Mr. Potter was very nice and professional. Checked on my problem with my car and told my my results and gave me an estimate...

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Jimmi
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Nissan Altima - Electric Problems - Orlando, Florida
great service very detail with finding the problem and giving all the solutions will call again when needed

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