We’ve had this question asked a few times recently and decided to investigate it. Which method of driving is more efficient; driving with your windows down and AC off or driving with your windows up and AC on? Today we find out.The battery in your car is a rechargeable battery. When you turn the key in your car to start the engine, the battery uses some of its charge to turn the engine over. It’s very similar to a pull starter on a lawnmower, the only difference is, a car’s starter is automated by an electric motor. In fact, some of the first cars had something much like a lawnmower’s pull starter – a crank in the front that one would turn that help get things going.Once the engine starts, it’s self-sustaining (as long as there is fuel) thanks to the combustion taking place inside the engine. While the engine is running, the alternator in the car (a small electrical generator) will recharge the battery using some of the power produced by the engine.If your battery dies thanks to leaving your lights on all night, the electronic motor in the car will not be able to turn the car over and it won’t start up.

However, if you were to roll the car down a hill while it’s in gear, the wheels turning will force the pistons to move and the car will start. Once started, the alternator will be able to recharge the dead battery.When you turn the AC on in your car, it uses energy supplied to it by the alternator. This energy is coming from the engine, which is using the fuel in your gas tank. fan not running in ac unitThe AC won’t run properly without the car started because the belt that engages the compressor (which is used to compress the coolant and make it cold) will only run with the engine started. build ac unitThis is the same belt that is responsible for running the alternator and charging your battery.outdoor air conditioner unit not runningTesting the effect of both methods (windows down, AC off versus windows up and AC on) has been done and debated by several different organizations.

One of the leading groups, the Society of Automotive Engineers, conducted a number of tests on the effects of AC versus windows rolled down on automobiles.The SAE found that running an air conditioner in an automobile decreased gas mileage by 5 to 10%. Stanford University and SAE both recommend driving with your car’s windows down if you are traveling on city streets. However, when on a freeway or highway, the drag produced by your windows being rolled down exceeds the efficiency drop by keeping windows rolled up and AC on. Both organizations recommend that you use your car’s AC when driving at speeds above 45 MPH.With that in mind, it’s probably best to do your driving in the early morning or later at night when possible. This is when the day is (usually) cooler. Driving with the A/C off and windows up is the most fuel efficient way to operate your automobile.Air conditioners and refrigerators work the same way. Instead of cooling just the small, insulated space inside of a refrigerator, an air conditioner cools a room, a whole house, or an entire business.

Air conditioners use chemicals that easily convert from a gas to a liquid and back again. This chemical is used to transfer heat from the air inside of a home to the outside air. The machine has three main parts. They are a compressor, a condenser and an evaporator. The compressor and condenser are usually located on the outside air portion of the air conditioner. The evaporator is located on the inside the house, sometimes as part of a furnace. That's the part that heats your house. The working fluid arrives at the compressor as a cool, low-pressure gas. The compressor squeezes the fluid. This packs the molecule of the fluid closer together. The closer the molecules are together, the higher its energy and its temperature. The working fluid leaves the compressor as a hot, high pressure gas and flows into the condenser. If you looked at the air conditioner part outside a house, look for the part that has metal fins all around. The fins act just like a radiator in a car and helps the heat go away, or dissipate, more quickly.

When the working fluid leaves the condenser, its temperature is much cooler and it has changed from a gas to a liquid under high pressure. The liquid goes into the evaporator through a very tiny, narrow hole. On the other side, the liquid's pressure drops. When it does it begins to evaporate into a gas. As the liquid changes to gas and evaporates, it extracts heat from the air around it. The heat in the air is needed to separate the molecules of the fluid from a liquid to a gas. The evaporator also has metal fins to help in exchange the thermal energy with the surrounding air. By the time the working fluid leaves the evaporator, it is a cool, low pressure gas. It then returns to the compressor to begin its trip all over again. Connected to the evaporator is a fan that circulates the air inside the house to blow across the evaporator fins. Hot air is lighter than cold air, so the hot air in the room rises to the top of a room. There is a vent there where air is sucked into the air conditioner and goes down ducts.

The hot air is used to cool the gas in the evaporator. As the heat is removed from the air, the air is cooled. It is then blown into the house through other ducts usually at the floor level. This continues over and over and over until the room reaches the temperature you want the room cooled to. The thermostat senses that the temperature has reached the right setting and turns off the air conditioner. As the room warms up, the thermostat turns the air conditioner back on until the room reaches the temperature. Imagine that you took an air conditioner and flipped it around so that the hot coils were on the inside and the cold coils were on the outside. Then you would have a heater. It turns out that this heater works extremely well. Rather than burning a fuel, what it is doing is "moving heat." A heat pump is an air conditioner that contains a valve that lets it switch between "air conditioner" and "heater." When the valve is switched one way, the heat pump acts like an air conditioner, and when it is switched the other way it reverses the flow of the liquid inside the heat pump and acts like a heater.