Is It Okay to Keep the Car Running with AC On for Two Hours?

[MilaDella]

Keeping the car running with the air conditioning on for two hours does not cause major issues, but prolonged low-speed engine operation can easily lead to carbon buildup, which may reduce power output. Precautions for using car air conditioning include: 1. Turn off the A/C during startup and rapid acceleration: Since the air conditioning (non-independent type) consumes some of the engine's power, it is best to turn off the A/C when starting the car or accelerating rapidly, and turn it back on after the car has gained speed. This prevents insufficient engine power during acceleration and startup while also saving fuel. 2. Avoid setting the temperature too low: Many drivers prefer setting the temperature very low in summer, thinking it is more comfortable. However, this is a misconception, as an excessive temperature difference between the inside and outside of the car can easily cause the driver to catch a cold, and excessively low temperatures may also increase the risk of arthritis for passengers. Normally, the cabin temperature should be 5°C to 6°C lower than the outside temperature. 3. Adjust the air vent direction: Based on the principle that cold air sinks and hot air rises, drivers should direct the vents upward when using the AC and downward when using the heater.

[ColtonAnn]

I've been driving long distances for over a decade and often keep the engine running with AC on for two-hour breaks at service areas, especially during scorching summers. While this does keep the car cool, it comes at a cost. The engine continuously powering the AC significantly increases fuel consumption—I estimate about 1 liter per hour, totaling 2 liters (burning dozens of yuan in fuel) for two hours. Prolonged idling can also lead to carbon buildup, reducing engine performance, though occasional use in new cars is less problematic. Once, while waiting roadside for a friend with AC on for two hours without shutting off, a mechanic later warned that excessive idling shortens spark plug life. My advice: If necessary, park in a ventilated spot with windows slightly open to prevent carbon monoxide poisoning; avoid making it a habit—prioritize shaded areas, turning off the engine and opening windows to save money and ensure safety. After all, cars are meant for driving, not as makeshift lounges.

[MacMicah]

As a budget-conscious car owner, I shake my head at this practice—it's such a waste of resources. Leaving the car running with the AC on for two hours unnecessarily burns fuel, as idling consumes more gas than driving at a steady speed. Doing the math, it wastes several liters of fuel, costing dozens of yuan. It's far more economical to park, turn off the engine, and find shade or roll down the windows for ventilation. Environmentally, it's also unacceptable, as the engine continuously emits exhaust, polluting the air. Although modern cars are durable, this habit accelerates carbon buildup, increasing long-term maintenance costs. I’ve tried briefly cooling the car with AC in open parking lots, but I turn it off after half an hour and switch to a manual fan or natural airflow. Why not save fuel and stay safe? Developing good habits not only maintains your car but also saves money.

[DiGrace]

Technically feasible: Running the car's AC for two hours while the engine is on is possible, as the engine-driven compressor can sustain cooling. However, prolonged idling may cause minor issues, such as normal battery charging but increased carbon buildup reducing efficiency. As someone who has repaired cars, I'm aware of the risks, including the danger of carbon monoxide accumulation in enclosed spaces. It's advisable to open windows for ventilation when parked to prevent accidents and to regularly check the engine's condition to prevent wear. Short durations are acceptable, but exceeding two hours increases the likelihood of malfunctions.