Is It Good to Run the Air Conditioner While the Car Is Idling?

[DeElliot]

Running the air conditioner while the car is idling is not advisable. When the engine is idling, the fuel does not burn completely, and the exhaust often contains a large amount of carbon monoxide. The carbon monoxide emitted with the exhaust may accumulate around the vehicle and enter the car through the air conditioning system. Additionally, with the windows closed while the air conditioner is on, the air does not circulate. Over time, the concentration of carbon monoxide inside the car will increase, posing a risk to human health. The power consumed by the air conditioner only accounts for a small portion of the engine's idle energy, but when idling with the air conditioner on, the engine not only drives the air conditioning compressor but also needs to maintain the normal operation of the power steering and brake booster pump.

[DiClaire]

I recently heard a mechanic talking about this issue. He said that idling with the air conditioning on is the most damaging to the engine. When the car is stationary, the fuel doesn't burn completely, and a layer of black carbon deposits can build up in just half an hour, clogging the fuel injectors and throttle body. Last week, I spent over 300 yuan cleaning the throttle body, all because of long-term idling. The air conditioning compressor is also a major problem area—the continuously rotating bearings are prone to overheating and deformation, and a single repair can cost over a thousand yuan. Even more concerning is insufficient engine lubrication, leading to dry friction between metal parts, which doubles the chance of a major overhaul in three to five years. Now, when picking up my kids from school in the summer, I turn off the air conditioning and open the windows five minutes early to ventilate.

[OliveLee]

Last year during a road trip, I personally tested the fuel consumption. A 1.5L sedan idling with the AC on for one hour consumed 1.8 liters of fuel, which amounts to about 15-16 yuan. The gas station attendant told me it's because the compressor is directly connected to the engine crankshaft, causing a drastic drop in power conversion efficiency during idling. The biggest waste is the cooling system—the radiator fan keeps spinning wildly, which also accelerates battery drain. Now, if I have to wait for more than ten minutes, I turn off the engine. Buying an iced drink from a roadside store is even cheaper than burning fuel. By the way, drivers with auto start-stop features should be extra careful, as frequent starts and stops consume more battery power.

[Hunter]

The news about sleeping in a garage with the AC on is not just a scare tactic. Carbon monoxide emitted by cars is heavier than air and can seep into the vehicle through gaps under the car in underground garages. Last week, the property management in our community posted a warning after a resident experienced dizziness and vomiting within half an hour of napping in the garage with the AC running. Even when parked outdoors, exhaust fumes can accumulate inside the car, making the elderly and children particularly susceptible to oxygen deprivation. Last time I took my daughter for a vaccination, I left the car running with the AC on while waiting for her mother to get the medicine, and my daughter turned pale. Now, I never idle with the windows closed for more than five minutes.

[TuckerRose]

Our ride-hailing fleet drivers all know from experience: don't set the AC temperature too low. At 24°C, the compressor works intermittently, but keeping it at 16°C long-term can cause the expansion valve to freeze and clog the pipes. Last year, our colleague Lao Wang's car lost cooling - inspection revealed a frozen and cracked evaporator. Nowadays in summer heat, we first open windows for ventilation before closing them and turning on AC, which is gentler on the vehicle than idling to cool down. A reminder for hybrid owners: using electric mode for AC is most economical and doesn't strain the engine.