Does keeping the car idling with the AC on damage the vehicle?

[VanAllison]

Keeping the car idling with the AC on can damage the vehicle. Here are additional details: 1. Warm engine: If you park after driving for a while, the engine temperature is relatively high. Turning on the AC for warm air will cause the RPM to increase slightly, but not significantly. 2. Cold engine: If you start the car when it's cold and then turn on the AC, the coolant temperature is very low. The engine needs to run at high RPM to quickly raise the engine compartment temperature and blow warm air, so the RPM will be relatively high at this time. 3. Hazards of prolonged idling with AC on: It is not recommended to idle with the AC on for extended periods as it increases the likelihood of carbon buildup. Regularly revving the engine or cleaning the carbon deposits is advised. Additionally, avoid idling with the AC on in enclosed indoor spaces or with windows tightly closed for long periods, as this can easily lead to dangerously high carbon monoxide concentrations inside the car, causing poisoning.

[HaydenRose]

I've been driving for over a decade and often idle with the AC on while waiting during summer, which does cause some harm to the car. There are two main issues: First, prolonged low-RPM operation leads to incomplete combustion and carbon buildup, especially in direct-injection engines, which over time reduces power and increases fuel consumption. Second, continuous AC compressor operation significantly wears out belts and bearings—I once had to replace a compressor because of this. However, occasional idling for under 30 minutes is generally fine; just avoid exceeding that duration. It's best to crack a window for ventilation to prevent dangerous carbon monoxide buildup. Also, older cars need battery attention—idling charges the battery slowly while the AC drains it, risking a dead battery that could leave you stranded.

[StJordan]

I've repaired many vehicles with issues caused by prolonged idling with the AC on, with the biggest hidden danger lying in the cooling system. At idle, the fan speed is low, radiator cooling efficiency drops, heat from the AC condenser can't dissipate, and the engine is prone to overheating. Especially in turbocharged cars, this is often the cause of coolant temperature warnings on the dashboard. Last year, one car's electric fan even melted and deformed, costing over a thousand yuan in repairs. Additionally, engine oil provides poor lubrication at low operating temperatures, doubling piston ring wear. To avoid this, it's best to turn off the engine every 20 minutes for a five-minute cooldown period.

[LeCali]

Last time when I drove my kid to the tutoring class, I slept in the car with the AC on for forty minutes. The next day, the engine felt sluggish when starting. The 4S shop told me it was a carbon buildup issue—the mechanic said the fuel doesn’t burn completely at idle, and the throttle body was covered in black sludge. Now I’ve learned my lesson: if I’m waiting for more than fifteen minutes, I turn off the engine or just roll down the windows for natural airflow. Actually, once the car’s interior cools down, using the outside air circulation is more convenient than the AC, and you don’t have to worry about overloading the battery. Older cars need extra caution—like my dad’s decade-old Jetta, whose battery died completely from idling with the AC on.

[DelCora]

From a mechanical perspective, idling with the AC on is most damaging to the engine and air conditioning system. When the engine runs at a low speed of 800 RPM, crankcase ventilation becomes poor, and oil vapor tends to form sludge. I've personally seen engines with valve cover interiors caked in asphalt-like deposits. The continuous operation of the AC compressor increases refrigerant flow pressure, making seals prone to leakage. Especially for cars over ten years old, aged rubber components can't withstand such strain. It's recommended to take a monthly highway drive to allow the engine to fully operate and clear carbon deposits. If prolonged idling is unavoidable, remember to set the AC temperature above 26°C to reduce compressor load.

[DiHayden]

Long-term idling with the air conditioning on is indeed harmful, but proper operation can mitigate the damage. I usually set the air conditioning to recirculation mode with the temperature around 25 degrees Celsius, which saves about one-third of the electricity compared to continuous cooling. As for the engine, if it's a direct-injection model, it's best to clean the intake system every 20,000 kilometers. Pay special attention to the battery; at idle speed, the power generation is just enough to cover the air conditioning consumption, making it impossible to charge the battery. Batteries older than three years are prone to sudden failure. Once, I measured the data and found that one hour of idling with the air conditioning consumes fuel equivalent to driving thirty kilometers, which is neither economical nor environmentally friendly. Now, if I have to wait for more than twenty minutes, I turn off the engine and wait in the shade.