is it ok to leave car running with ac on

[BriellaAnn]

Yes, it is generally okay to leave your car running with the AC on, but it should be done with caution and for limited periods. The primary risks are not mechanical failure but rather fuel waste, potential engine wear from extended idling, and the critical danger of carbon monoxide poisoning in enclosed or poorly ventilated spaces.

Modern car engines are designed to handle the load of the air conditioning compressor at idle. However, idling for more than 30 minutes can be inefficient. The engine runs rich (using more fuel), and oil pressure is lower than when driving, which isn't ideal for long-term engine health. The most significant hazard is carbon monoxide (CO), a deadly, odorless gas that can seep into the cabin from the exhaust system, especially if there's a leak or the car is in a garage.

For short waits, like waiting for someone for 10-15 minutes, it's perfectly safe in an open area. For longer periods, the risks outweigh the benefits. It's more efficient to turn the engine off and seek a cooler location.

Supporting Data Point	Source / Context
Idling for more than 10 seconds uses more fuel than restarting the engine.	U.S. Department of Energy
An hour of idling can burn between 0.2 to 0.5 gallons of gas, depending on engine size.	EPA (Environmental Protection Agency)
At least 430 people die annually in the U.S. from unintentional CO poisoning.	CDC (Centers for Disease Control and Prevention)
Over 50,000 people visit the ER each year due to accidental CO exposure.	CDC
Carbon monoxide can build up to dangerous levels even with the garage door open.	NHTSA (National Highway Traffic Safety Administration)
Prolonged idling can cause damage to engine components like cylinders and spark plugs.	Society of Automotive Engineers (SAE)
Idling a car for one hour emits about 20% more CO2 than driving for the same duration.	European Energy Agency
Most modern AC systems can maintain a cool cabin for 15-20 minutes after the engine is off if recirculation is on.	Automotive Engineering International

[Zachary]

I do it all the time when I'm waiting to pick up my kids from practice. The key is to be outside, never in a garage. I figure the comfort is worth the few cents in gas. My main worry is always the exhaust, so I make sure I'm parked somewhere with plenty of fresh air moving through. For a quick 20-minute wait, I've never had an issue with the car.

[Deborah]

From an environmental standpoint, it's a wasteful habit. Idling engines contribute unnecessarily to air pollution and greenhouse gas emissions. If you're going to be stationary for more than a minute or two, it's far more responsible to turn off the engine. The brief comfort of air conditioning doesn't justify the environmental cost, especially when you could simply park in the shade or roll down the windows for a bit.

[SanClayton]

Think of it like this: your engine is working but not getting up to its optimal temperature. This can lead to something called "engine fouling" where fuel doesn't burn completely. It's fine for short stops. For longer waits, I'd recommend finding a shady spot, turning off the car, and using a sunshade. If you must idle, ensure the air intake is set to recirculate to reduce the load on the AC compressor and save a little fuel.

[ReaganRose]

As a mechanic, I see the long-term effects. While your car can handle it, idling for hours on end isn't great. It puts minimal wear on the AC system itself, but the engine isn't operating efficiently. You're not getting the best oil circulation, and fuel dilution can become a slight issue over time. The real message is safety: never, ever do this in an enclosed space. A well-maintained car in an open parking lot? You're probably okay for a reasonable amount of time.