Does Car Air Conditioning Waste Gas

Modern car drivers appreciate many different features, which are now commonly seen as standard on production cars. Electric windows, heated seats and air conditioning may all once have been seen as a luxury but demanding drivers have now forced manufacturers to think differently. Drivers may not always be certain, however, what the impact of using these features can be on the overall performance of the car. Many drivers believe, for example, that the air-conditioning in a car greatly increases the consumption of fuel. So does air-conditioning really waste gas?

Common perception

Many drivers believe that the air conditioning unit is absorbing fuel when in use. This is a perfectly reasonable assumption to make. An air conditioning unit will require energy to function, and that energy is ultimately derived from the fuel supply. It seems sensible, therefore, that if you use additional systems like the air conditioning, then you will be placing more demand on the fuel. This may not, however, actually be the case.

Comparison with the alternative

Drivers turn the air conditioning on to cool down the car's interior on a sunny day. When the sun is beating down onto a car's window, the temperature inside the car is going to increase, very quickly making it very unpleasant for the occupants. The air conditioning helps prevent this. If you don't have the air conditioning on, the only alternative is to have the window open. Studies have shown that when you compare the fuel consumption of a car with the windows shut and the air-conditioning on with that of a car with the windows open and the air-conditioning off, the fuel economy, there is no real difference. This is because the car with the windows open uses more fuel to maintain the same speed as the other car due to the increased drag on the car, caused by having the windows open.

The alternative view

A report published by the National Renewable Energy Laboratory (NREL) concluded that using the air conditioning in your car does decrease your fuel efficiency. This study was not concerned with the energy used by the air conditioning system so much, but more about the overall increase in fuel consumption brought about the weight of the additional equipment. The NREL concluded that the air conditioning unit weighed down the car throughout the year, forcing an increase in fuel consumption.

The answer

Under certain conditions, using the air conditioning in your car could be seen as having a negative impact on your car's gas mileage, if you assume that you could happily live without it. In the middle of the heat of summer, however, unless you can cope with the windows shut, it seems unlikely that you will see any real difference in performance. There are a number of ways that you can get the best performance from your air conditioning system however:

  • Service the system annually
  • Park the car in shady areas, so that the air conditioning doesn't have to work so hard when you first start the car.
  • Turn air conditioning off around town if you are stopping and starting a lot, and open the windows or if you are parked.
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