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Does AC Waste Gas: Myth Or Fact?

by Kelvin Yates

Someone probably has said to you to turn off the air conditioning in your car to save fuel. But does AC actually waste gas? In short, yes. But maybe “waste” is the wrong word since it’s not wasted now, is it? It gives you that sweet cool air during a hot summer day. Rather, the correct term would be it makes your car use more gas.

Okay, maybe that’s just us being pedantic. But in short, yes, the air conditioning system in your car does use gas. We’ll talk about why and how it uses gas, whether or not you should turn it off to save fuel, and other fuel-saving measures you should know.

Does AC Waste Gas: How Car AC Works

Now you know the answer to the question “does AC waste gas?” is yes. But how does it work? Why does it make your car use more gas?

Air conditioning works pretty much the same way in all cars. It works similarly to your home air conditioning as well, by using a refrigerant to cool the air. Here are the components in your car’s air conditioning and how they work:

  1. Refrigerant. First and foremost is obviously the refrigerant, which is a chemical that produces a cooling effect as it expands or vaporizes. Cars typically use the R-134A refrigerant or the R-1234YF. But some cars may also still use the R-12 or Freon as the refrigerant (to learn more, check out our explainer in how to check freon in car and how to put Freon in car).
  2. The compressor is the device that compresses the refrigerant. Once the refrigerant transforms into high-pressure and high-temperature gas, it will flow into the condenser.
  3. A condenser then removes heat from the refrigerant and pushes it into an expansion valve or sometimes called an orifice tube.
  4. At the expansion valve or orifice tube, the refrigerant returns to its original gas state. It then travels into a receiver/drier or accumulator.
  5. The receiver/drier or accumulator is called as such because it dries the refrigerant by removing moisture. It’s built into the condenser, and afterward, it will transfer the gas into the evaporator.
  6. Finally, you get to the evaporator which dissipates even more heat from the refrigerant passing through the evaporator core.
  7. A fan or a blower will then blow air through the evaporator. This results in cool air being blown through your car’s air conditioning vents.

The video above will give you a better idea of how the entire system works. As mentioned, it works the same way virtually in all cars.

Does AC Waste Gas: Why It Uses Gas

So, that’s how the air conditioning system works in your car. But wait, how does AC waste gas? How exactly does it affect fuel consumption? Well, it’s obviously because you need something to power the system.

The battery in your car isn’t powerful enough to do this, at least, for not an extended period. So, the job of powering the air conditioning system falls to your car’s drive belt, or often referred to as the serpentine belt.

Does AC Waste Gas

The serpentine belt is a long belt that powers various components, such as the alternator, power steering pump, and yes, the compressor of your car’s air conditioning system. Since it runs off the engine’s power, using the air conditioning will increase the engine’s workload.

All this means that your engine has to work harder to accommodate the power demand of the air conditioning system and other electrical components. Since more power is needed, you’ll need to work the engine harder by pressing the gas pedal harder.

When you do, you will use more gas. In a nutshell, your AC system uses the alternator as its power source, and the alternator is powered by the engine. This increases the load on your engine, making it use more gas.

Does AC Waste Gas: Can I Save Gas By Turning Off The AC?

Yes, you can. It may not be noticeable in most modern cars, but in older cars – especially with smaller engines – you can feel the car accelerate faster if the air conditioning is off. This is confirmation that air conditioning does indeed put more load on the engine and takes away power.

Since acceleration is slower, the engine has to work harder to get to speed. For example, let’s say without the AC you only need 40% throttle to get to 60mph quickly. However, with the AC on, you’ll probably need 50 – 60 percent throttle, which consumes more fuel.

It’s not noticeable in modern cars since they’re usually more powerful and efficient. But the effect is there, and you can save fuel by turning off the AC. ConsumerReports states that you’ll save somewhere around 1 – 4MPG by turning off the AC, depending on your car’s make and model.

However, we argue this isn’t worth it. Sure, you save fuel, but you’ll be left without nice cool air blowing through the vents. Not a big deal if it’s cold outside, but on a hot sunny day you’ll be sweating like a pig. Pigs don’t actually sweat, but that’s not the point here.

One scenario we think turning off the AC is worth it is when you’re low on gas and there’s no gas station in sight. In this situation, you’ll obviously want to save as much gas as possible. Speaking of fuel economy…

Does AC Waste Gas: Other Ways To Improve Fuel Economy

Turning off your AC to save fuel means you’ll have to sacrifice comfort for MPG. We don’t like that, I personally like to stay nice and cool, and comfortable while driving. So, here are the other ways you can save fuel – without sacrificing driving comfort!

1. Drive Steadily

Your driving style is probably what affects your car’s fuel economy the most. If you tend to constantly hit the gas and the brake, it’s time to stop that! You’ll need to drive more steadily.

Case in point, this test below between the Toyota Prius (an economical hybrid car) and the BMW M3 (a performance sedan with a V8) in an economy run done by Top Gear shows how your driving will affect fuel consumption. Skip to 3:35 if you want to see the test:

As you can see, the way you drive will affect fuel economy greatly. Driving steadily means you’ll need to step on the gas less often, and when you do, you’ll step on it lightly and gradually. This reduces fuel usage as you’re not accelerating as often and as hard.

For example, if you’re on the highway, keep a constant speed of 50 – 55mph. Even if the road in front of you opens up, keep it steady. Chances are you’ll hit traffic soon enough anyway, which means you’ll have to brake, and then accelerate up to speed again. This consumes more fuel than when you drive at a steady speed.

Easy enough on the highway, but what if you’re driving in the city? Well, you’ll need to anticipate. If you see a speed bump, traffic, another car trying to pull out, or any obstacle that will require you to brake, then there’s no need to accelerate excessively.

This is because you’ll need to brake soon anyway which means you’ll lose speed. Afterward, you’ll need to accelerate again, which means using more fuel. By anticipating what’s in front of you and driving more steadily, you don’t have to accelerate as often, reducing overall fuel usage.

2. Make Sure Your Tires Have Correct Pressure

Every carmaker will have a recommended tire pressure for each car. This number is usually somewhere around 32 – 36 PSI, and you can find the exact recommendation on the driver’s door or in your owner’s manual. Once you find that number, make sure your tires have the correct tire pressure.

If the tire pressure is too low, this means the tires are deflated. And when tires deflate, the contact patch between the tires and the road will increase. This results in more drag, which slows down the car during acceleration and it has to work harder to get to speed. All this means you will have to use more energy to get up to speed, which uses more fuel.

With the correct tire pressure, your car will have an optimum contact patch. Not too little that it compromises handling and safety, but not too much that fuel consumption suffers. Additionally, correct tire pressure will prevent excessive tire wear and prolongs your tires’ lifespan.

Many modern cars now have a tire pressure sensor, so you can monitor it directly in the car. If your car doesn’t have it, tire pressure gauges are cheap and easy to use. Simply remove the tire’s valve cap, attach and press the gauge to the valve. Make sure there’s no hissing sound, and it will immediately take a reading.

Check the tire pressure for all four tires, then fill the tires with air as necessary. You should check it at least once every three months. But we recommend checking it more often if you often put a lot of load in the car.

3. Align Your Tires

Drag is the enemy of your car’s MPG. And speaking of drag and tires, you should also check your wheel alignment periodically. Alignment refers to the angle of your wheels to make sure the vehicle’s travel is straight and true. Each manufacturer has its recommended angle.

Over time, the wheels may become misaligned. Not only this will make it difficult to keep the car straight, but it can increase tire drag since they’re not on the same angle. And as mentioned, increased drag will worsen fuel consumption.

Does AC Waste Gas

That’s arguably the least of your problems, as misaligned tires can increase tire wear, and the wear may become uneven. This could lead to one tire being more worn than the other over time.

Driving on unevenly worn tires is like driving on mismatched tires: it will increase fuel consumption and can cause excessive wear on the transmission and possibly suspension components as well.

All of the consequences above are good reasons for you to align your tires regularly. Most cars will need a tire alignment around every 6,000 miles. Front-end alignment typically costs $65 – $100, and an alignment for all four wheels will cost between $100 – $150. If you want to learn more about wheel alignment and find out the cheapest place to align your tires, check out our comprehensive guide here.

4. Keep Up With Routine Maintenance

We can’t stress this enough: keep up with your car’s routine maintenance. This includes oil and oil filter change, air filter change, spark plugs replacement, and more. All of this affects your car’s performance, and ultimately, it will affect fuel consumption as well.

For example, spark plugs are devices that create a spark that ignites the fuel and air mixture in your engine’s cylinders. When the fuel and air mixture combusts, it will push the pistons inside your engine. This is an oversimplification, but in a nutshell, this is how your engine creates power.

If a spark plug is worn, it won’t be able to ignite the mixture, or at least, not efficiently This will often result in a misfiring engine. Engine misfires will cause it to hesitate, meaning you’ll have to step on the gas more to get the same amount of power, which uses more fuel.

Does AC Waste Gas

Meanwhile, the engine oil will turn sludgy over time if you don’t change it. When it’s sludgy, the engine components will have to work harder since there are more grinding and resistance. Not only this will increase fuel consumption, but it will cause excessive wear.

The routine service interval varies depending on your car’s make and model. Some cars require a service every 5,000 miles, while others can go as far as 10,000 miles without one. Check your owner’s manual to find the recommendation for your car, and keep up with it! Learn more about basic car maintenance here.

5. Stay Light

The weight your car has to lug around also affects its fuel consumption. The more weight your car has to carry, the more fuel it needs to get going. If you have any unnecessary items or accessories, it’s time to remove them from your car.

Such items include roof racks, cargo boxes, and bike racks. Not only do they weigh down the car, but they can also affect the car’s aerodynamics as well which will ruin gas mileage. Only keep the absolute necessities such as your emergency kit in the car.

6. Keep Idling To A Minimum

By definition, idling will reduce your miles per gallon since, well, you’re not doing any miles when you’re idling. So, keeping idling to a minimum will help to increase your car’s MPG.

This is why a lot of modern cars now have a stop-start system, where the car will turn off on its own when it comes to a complete stop. A car consumes about a liter of fuel per hour when idling. When it’s off, then obviously it won’t be consuming any fuel.

If you don’t have a stop-start system in your car, then you can manually turn it off. But we recommend doing this only when you know you’re going to be idling for some time. For example, when you pull up at a red light that will take more than a minute to turn green.

Otherwise, don’t worry too much about it. Turning your engine off and on too frequently may even cause it to consume more fuel. Not to mention, it will put additional strain on your battery, causing it to go flat much quicker. Just make sure you don’t idle when unnecessary, such as when you’re waiting in your car.

Does AC Waste Gas: Questions & Answers

Got any more questions about your car’s air conditioning system? The answer you’re looking for might be below:

How Often Should I Service My Car’s AC?

Usually about once a year. If your car’s air conditioning system is healthy, all your technician will need to do is refill the refrigerant, clean the condenser, and possibly replace the cabin filter. This costs anywhere between $150 – $300 depending on your car’s make and model.

The technician will also likely test if they suspect there’s a leak. The first thing the technician will do is measure the pressure inside the system. If the pressure doesn’t match the manufacturer’s specification, then you may have a leak.

If the technician suspects a leak, the next thing they will do is hook up your car to a refrigerant recovery system to drain any harmful gases in the system. Afterward, they will check the hard lines for signs of obvious cracks. If there are no cracks, they’ll check other components.

They’ll check all the components including the compressor and condenser. If they’re faulty, then you will likely need to replace them. A car AC compressor costs between $990 – $1,200 to replace. While the condenser costs around $450 – $950 to replace depending on your car’s make and model.

Will My AC Ever Need Replacing?

As in the entire system? No, but the parts and components we mentioned above may need replacing over time. But don’t worry, air conditioning components usually last quite a long time.

For example, the air conditioning compressor is typically rated to last around 8 – 10 years. Meanwhile, carmakers suggest that the condenser and evaporator in their cars will last for around 10 – 15 years. Excluding external damages that may happen to the components, of course.

So, if you bought a new car, and you’re planning to keep it for less than 10 years, you don’t have to worry about replacing these components any time soon. Provided that you maintain your air conditioning system.

How Do I Maintain My AC?

Car air conditioning maintenance is pretty simple and there’s not a lot that you will need to do. Simply do the following things:

  • Clean or replace the cabin filter. This usually needs replacing every 30,000 miles, but check with your owner’s manual to get the exact recommended interval.
  • Clean dust and debris from the air vents. This will prevent them from getting into the AC system which can clog and damage the system.
  • If you live in a cold area where it’s too cold to turn the air conditioning when you drive, turn it on for 10 minutes once a week. This will help to maintain gas pressure inside the system and keep the compressor working properly.
  • Run the defrost once a week for 5 – 10 minutes to prevent mildew and other unpleasant odors, and to clear away excess moisture in the air conditioning system.
  • Service it regularly, at least once a year. A professional technician may be able to detect a leak or other faults you might not notice. Then they can tune up the system and make sure it runs smoothly.

How Does The Heater Work?

Good question, the heater is actually a somewhat separate system from the air conditioning. The heater uses a heater core, which is a device that looks like a smaller version of your car’s radiator. But how does it work?

The heater core is part of your car’s cooling system. When you turn on the heater, the system will divert some of the hot coolants from your car’s engine to the heater core rather than directly back to the car’s radiator.

Mercedes-Benz CLS AC Vents

A blower will then blow air through the heater core, resulting in hot air that gets blown into your car through the air vents. The coolant will travel into the radiator, and the heater core takes in new hot coolants from the engine to maintain the heat in your car.

This is why when you cold start the car and immediately turn on the heater, the air isn’t immediately hot. This is because the coolant is still cold, which means the heater core isn’t hot yet and the air blowing through it won’t turn hot. You can learn more about the heater core in this post.

Can You Save Gas by Not Using Your Car’s AC?

  • While operating, a car’s AC system does add a slight load to the engine, which could slightly increase gas usage, according to David Bennett, manager of repair systems for the American Automobile Association (AAA).
  • The added gas usage from using a car’s AC system would not be noticeable for most drivers, so the savings from not using the AC would be minor and not realized by most consumers.
  • Whether turning off the AC to save gas (and helps you with learning how to save gas) depends on the vehicle’s specific configuration and the type of AC compressor it uses, so it’s difficult to give a definitive answer without considering these factors.
  • Opening the windows and driving with them down reduces fuel efficiency even more than blasting the AC because it creates excess drag on the vehicle, which increases resistance.
  • If you want to significantly improve your MPG, forget about the AC and focus on other ways to improve fuel economy, such as maintaining proper tire pressure (you can learn more in our explainer on the tire pressure for Honda CRV), driving conservatively, avoiding excessive idling, and following the manufacturer’s recommended maintenance schedule.
  • Improperly inflated tires have a greater impact on gas mileage than using the AC, as underinflated tires have a higher rolling resistance that reduces fuel economy.
  • Rapid acceleration and hard braking can lower fuel economy by 15 to 30 percent at highway speeds and 10 to 40 percent in stop-and-go traffic, so it’s better to drive conservatively to save gas.
  • An idling car consumes one-quarter to one-half gallon of fuel per hour, so it’s best to avoid excessive idling and turn off the engine if you’ll be stopped for a minute or more and if it’s safe to do so.
  • Maintaining a vehicle according to the manufacturer’s recommended service schedule can also improve fuel economy, so it’s essential to follow these guidelines to ensure optimal performance.
  • While turning off the AC might save a little bit of gas, it’s not a significant enough amount to make a considerable difference, so it’s best to use the AC when necessary to stay comfortable while driving.

Does AC Waste Gas: Wrap Up

So, does AC waste gas? The answer is yes. When you turn on the air conditioning in your car, it will put more load on the engine since the system runs off the drive/serpentine belt which is powered by the engine. This extra load on the engine means it will need more fuel to run, which means your car consumes more fuel.

Turning off the air conditioning in your car will increase the gas mileage, helping you to save fuel and money. But we feel like the tradeoff isn’t worth it unless you’re low on fuel and not sure when you will see a gas station. Instead, there are other fuel-saving measures such as changing your driving style, having sufficient tire pressure, and keeping up with routine maintenance to keep the engine running smoothly.

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