AC is one of the components that directly depends on engine power for its working. It is the single largest auxiliary load on a vehicle of any kind, whether fuel-driven or electric.
Now it means, if AC depends on the engine for its working, it will increase the fuel consumption.
Now, there kicks in some criteria which will affect the fuel consumption due to AC.
Before heading to that, first, have a look at the working of an AC.
The general principle behind the working of a car air conditioning system is that it converts the refrigerant from liquid to gas and gas to liquid. This cycle repeats until there is a shortage of refrigerant.
It seems very simple, but it isn’t.
So, you should know about the components of a car air conditioning system to better understand its working.
The car air conditioning system includes two different functions; we can differentiate them as
These two sections are separated depending on the pressure state of the refrigerant.
Firstly taking the high-pressure side, it includes:
The function of the compressor is that it compresses the low pressure, low-temperature gas into a high pressure, high-temperature gas.
It works over a pulley that is attached to the crankshaft of your car engine via a belt.
Now, this is how AC depends on engine power for its working.
This high-pressure, high-temperature refrigerant moves on to the second component of the car AC system, the condenser.
The function of a condenser is to lower the temperature of a hot pressurized refrigerant.
As soon as the hot pressurized refrigerant reaches the condenser, its work is to lower the temperature. This condenser works like a radiator, and as the refrigerant passes through the condenser, it gets cooled down.
From here on, this cold pressurized refrigerant will move on to the receiver, also known as a dryer.
The car AC receiver or dryer comprises several filters and desiccants.
Filters help to filter out any impurities, such as dust particles or metal particles. On the other hand, the desiccant helps to make the refrigerant moisture-free.
Desiccants are made of water-absorbing substances and hence absorb all the moisture from the refrigerant.
The cold pressurized gas from the condenser enters the receiver through the inlet point. After entering, it passes through a series of filters and desiccants. After this, now refrigerant exits through the outlet point and reaches the expansion valve.
From now onwards, the lower pressure side comes into effect.
An expansion valve checks the limit of refrigerant that can move forward through the AC system. The expansion valve works similar to a sprinkler nozzle which converts a high-pressure beam to a low-pressure mist.
Since the expansion valve falls under the lower pressure side, it reduces the pressure of the refrigerant. In addition to pressure decrement, it also cools down the refrigerant even further.
Some car air conditioning systems have an accumulator. An accumulator works similar to a dryer, but it comes between the compressor and evaporator. When it comes with the accumulator, then the expansion valve is also replaced by an orifice Tube.
The main difference is in their opening. The expansion valve has a fixed opening hole, while Orifice Tube has a regulated one that depends upon the temperature in the evaporator.
Now from here on, the cold and low-pressure refrigerant moves on to the evaporator.
As you can guess from its name, it has something related to evaporation. The evaporator converts the refrigerant again into the gaseous state.
When the cold and low-pressure refrigerant enters the evaporator, it comes in indirect contact with hot air, absorbs the heat from the air, and turns into a gaseous state.
Moreover, the air becomes cold as the refrigerant absorbs the heat.
Now, this cold air reaches your car cabin through the AC vents.
So we can sum up the working of car air conditioning system in these simple steps.
Step1: The compressor compresses the refrigerant and makes it pressurized and hot.
Step2: From the compressor, it reaches the condenser. The condenser lowers the temperature and hence makes the refrigerant cold and highly pressurized.
Step3: From the condenser, it reaches the receiver. The receiver filters and removes moisture from the refrigerant.
Step4: Then, from the receiver, the refrigerant reaches the expansion valve. Its function is to decrease the pressure and temperature of the refrigerant.
Step5: From the receiver, the cold and low-pressure refrigerant enters the evaporator. The refrigerant here absorbs the heat from the surrounding air and changes back to gaseous form. On the other hand, the air turns cold and is ready to be blown into the car cabin.
Initially, when the automobile air conditioning system was introduced, R-12 was used as the refrigerant.
R-12 is a chlorofluorocarbon-based refrigerant that is very effective in cooling, and also it is non-flammable. Although it does not cause any direct harm to humans, it affects the Ozone layer. Hence, later on, it was replaced by R-134a, which is a hydrofluorocarbon-based refrigerant. It does not affect the Ozone layer.
Today most of the manufacturers use R-134a as the refrigerant in car ac.
If you park your car in direct sunlight, then do not turn on the AC as soon as you sit in the car. Firstly drive for a few minutes with windows open this will remove the excess hot air from the car. Hence your car engine will not get much load. Doing this saves some fuel which otherwise your car AC will use to cool down that high-temperature air.
If you don’t necessarily need AC, it’s better to open windows and the sunroof when you drive in the city. You can close the windows and use the ‘Re-circulating function’ of your car AC once your car temperature decreases. This system cools air already present in the car.
There are two scenarios, either roll up the windows and turn on the AC or roll down the windows and turn off the AC.
You will not get many benefits even if you turn off the AC and open up your windows.
No benefits because most cars have an aerodynamic design. When you open your car windows, the air will apply extra pressure on your vehicle in the direction opposite to its motion.
Hence, the car will need more power to maintain the same speed, and more power means more fuel consumption.
So it’s better to enjoy cold AC air, rather than the hot air of the highway when the fuel consumption in both cases is almost the same.
Even if you are using a defroster, shut it off as soon as the windows are clear.
Yes, the car AC increases fuel consumption. In other words, we can say that a car air conditioning system decreases the mileage of a car.
The amount of fuel consumption can increase or decrease depending upon several factors like the health of the air conditioning system and many more.