devices that run the ac

Figure 1: The car engine and compressor.

In summer, many people like to park their cars on the side of the road, opening the air conditioner for a long time. But during this process, there is an increase in fuel consumption. In fact, it will lead to other problems and pitfalls.

The working conditions of the auto air conditioner are divided into cooling mode and heating mode. In winter, the internal combustion engine burns and generates heat while we are driving, and the air conditioning system uses pipes and a blower system to blow hot air into the cab.

In summer, the refrigeration compressor is required to run the air conditioner. So where does the compressor power come from? It is the engine.

As shown in the figure 1, when the air conditioner is started in summer, the crank of the engine rotates while the compressor is driven by the belt, and the oil consumption will be significantly higher.

At the same time, the mobile compressor rotates, so the kinetic energy of the engine may be compromised. If it’s coupled to the transmission, the power goes down, and so does the power of the wheels. The smaller the engine, the more significant the reduction in power.

Car Heater

In heating mode, you should stop the car after driving temporarily. For example, after work, you open the air conditioner in the car, then the engine temperature is very high. If you use heating mode, the speed will rise slightly, but not too high.

In cooling mode, if you start the car and open the air conditioner, the water temperature is very low, the engine needs to run at a high speed to improve the temperature of the engine, then the speed is relatively high.

Car AC

In summer, whether the heating system or air conditioner operates, the engine speed is very low, and the idle speed is higher than that when the air conditioner is stopped. This is because the compressor can be fully used at the low speed.

car ac starts

Figure 2: Someone is starting the ac.

You should note that long periods of engine idling at low speeds will greatly increase the probability of carbon accumulation. There are many problems associated with carbon increase, one of which is to stop the car and turn on the air conditioner.

As we know, the damage of carbon deposition will affect the work of the nozzle and cause poor atomization. In addition, carbon increase may affect the mixture of oil and gas, thus adding fuel consumption, causing power damage, engine power reduction, and influencing the ignition timing. The engine has difficulty starting, leading to shaking.

Excessive Carbon Deposits

It’s the engine idle speed that the throttle is critically closed and the air intake is insufficient. In this state, in order to keep the idle speed stable, it is necessary to increase the injection amount, and it is in the thickened injection state.

At this point, due to the extremely thick mixture, the engine will accumulate more carbon. If you open the air conditioner at engine idle speed, the engine operates at low speed with load, so as to avoid shutting down.

In order to maintain the stability of the engine operation, its speed needs to be appropriately improved. In the case of the idle speed, the air intake is still relatively limited. Increasing the engine's power output further by multiple fuel injection, and the combination gas is thickened, which results in more carbon deposition.

Affecting the Engine

When the engine is seriously affected by carbon deposition, it will affect the oil lubrication, the engine, and the oil blocks the three-way catalytic converter and oxygen sensor, thus leading to a more severe vicious cycle. The carbon deposition will affect the running state of the engine and eventually lead to engine failures.

Carbon Monoxide Poisoning

For a long time, if you use the air conditioner with engine idle speed, leading to a large amount of carbon monoxide. This carbon monoxide is slightly lighter than the air. When there is no wind outside, carbon monoxide will gather around the car and may be re-inhaled into the air conditioning system, causing safety accidents due to a lack of oxygen.

What’s worse, if you keep the car windows closed while the air conditioner is on, there will be no air circulation in the car. Over time, carbon monoxide levels in cars can get higher and higher, posing a health hazard.

If the carbon dioxide emitted by the passengers increases while the oxygen is gradually decreasing, the passengers will be poisoned and lose consciousness, leading to their asphyxiation and deaths. What is more serious is that it is difficult for people in the car to perceive whether they are poisoned. When they feel sick, they are unable to open the door for ventilation.

The air conditioner consumes a small fraction of the engine's idle power output. However, the engine not only drives the air conditioner compressor, but also needs to maintain the normal operation of the steering/brake booster pump.

They are extra functions when the car stops, so it is actually a waste of power. In this respect, the engine idle speed only provides energy to the air conditioner compressor.

using the car ac

Figure 3: Somebody is adjusting the outlet of the car ac.

Damage the Car

If you use the air conditioner when stopping the car, it will make the gasoline burn partially, and cause the engine power reduction, and the power transmission is uneven.

If the carbon deposition is too high, it will also cause cylinder vibration. There will be noise when accelerating, causing damage to the piston and crankshaft, and high engine temperature. As a result, it seriously affects the safety of the car.

Abnormal Sound under the Car after Stop

The turbocharged car has the function of delaying heat dissipation. You will hear the sound of fan rotation after extinguishing it. It is specifically designed to protect the turbocharger.

The exhaust pipe dripping is not a fault. In fact, it is also a normal phenomenon, and there is no need to check.

The temperature of the exhaust system will be extremely high. When the temperature drops rapidly after shutting down, you can hear an abnormal sound. The exhaust pipe is based on the same principle.

But if you hear the sound when driving, you need to get it checked out and repaired.


In a word, it is not recommended to use the air conditioner after stopping the car for a long time. Under this circumstance, the probability of carbon deposition will be higher. If you do, you should increase the rotation speed and clean the carbon regularly. In addition, you cannot close all the windows, because it is easy to cause high carbon monoxide concentration inside the car.

Related Info

5 Reasons Why Your Car AC Not Cooling

Car AC Compressor Troubleshooting-- Best Suggestions