Air conditioning makes driving more comfortable, but it can also affect your fuel economy. When you turn on your car air conditioner, you’re not just cooling down the cabin; you're also putting extra work on your engine.
Want to know what’s really going on under the hood? At Universal Technical Institute (UTI), students in our Automotive Technology program learn how systems like car air conditioning work and how to diagnose, repair and service them. If you're curious about vehicles and how to keep them running efficiently, this could be the career path for you.1
Whether you’re a car enthusiast or pursuing a career in automotive maintenance, understanding how AC systems affect fuel efficiency can deepen your technical knowledge and improve the way you operate and maintain vehicles.
How Does a Car Air Conditioner Work?
A car air conditioner relies on a closed-loop system made up of three main components: the compressor, condenser and evaporator. Here’s how they work together to keep your vehicle cabin cool:
- Compressor: Powered by the engine via a drive belt, the compressor pressurizes the refrigerant gas and circulates it through the system. It’s often considered the heart of the AC system.
- Condenser: Located at the front of the vehicle, the condenser cools the high-pressure refrigerant gas and turns it into a liquid as it passes through a series of coils.
- Evaporator: Inside the cabin, the evaporator absorbs heat from the interior air. As the refrigerant evaporates, it removes heat and humidity, blowing cool air through the vents.
All these components are powered by the engine. So, when the car air conditioning system is running, it draws power, resulting in increased fuel usage.
Students in automotive training programs often study systems like these early in their coursework. For example, in UTI’s Automotive Technology program, courses cover how air conditioning systems function, including refrigerant handling, system diagnostics and component repair. Understanding how the compressor, condenser and evaporator work together to deliver cool air is foundational knowledge for those training to service modern vehicles.
What Causes an Air Conditioner To Burn Fuel?
Running your car’s air conditioning system adds an extra load to the engine. When the AC compressor engages, it draws mechanical energy from the engine’s crankshaft to compress and circulate refrigerant through the system. This process requires additional power, particularly in systems that use a belt-driven compressor.
To account for this added workload, the vehicle’s engine control unit (ECU) adjusts the fuel injection rate. It sends more fuel into the combustion chambers to maintain engine performance and prevent stalling. This compensation ensures that other vehicle functions — such as acceleration, steering and braking — aren’t negatively affected by the AC’s energy demand.
The result? The engine burns more fuel to support the system, especially in stop-and-go traffic or when idling, where efficiency is already reduced. Over time, this added consumption can lead to noticeable dips in miles per gallon, making air conditioner use one of several factors that influence overall fuel economy.
How Much Fuel Economy Is Lost?
The extent to which a car air conditioner affects fuel economy depends on several variables, such as vehicle type, outdoor temperature and driving behavior. However, multiple studies have attempted to quantify its impact.
A study published in the Transportation Research Record found that air conditioner use could reduce fuel economy by up to 21% in urban driving and between 6–10% on the highway. The findings noted that the level of impact varied depending on vehicle size and whether the system was operating in recirculation mode.
Similarly, a report by SAE International examined real-world vehicle operation and determined that car air conditioning use could lower fuel economy by 5–25%, with the largest reductions observed at lower driving speeds.
While these percentages may seem small on short trips, they can add up quickly over time, especially for drivers in hot climates who use car air conditioning services frequently.
Drive Your Auto Maintenance Career Prep Forward With UTI
If you’re fascinated by vehicle systems and want to explore the science behind fuel efficiency, air conditioning and more, UTI’s Automotive Technology program is a great place to start. You’ll receive hands-on training with real vehicles, learn from experienced instructors and develop skills that today’s employers look for in the automotive industry.18
Ready to take the driver’s seat in your career path? Train for a future in the garage, not behind a desk. Request more info and an Admissions Representative will reach out. You can also take the first step today and fill out an application!
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