"What does this weird button on my AC system do?"
John Goreham's picture

What's That Button Do? Use Your Modern Prius Heating and Cooling For Maximum MPG - Here's How

"What does this weird button on my AC system do?" This is a common question new owners of Prius cars have. We can help.

The Torque News staff is very active in the Facebook Toyota Prius Owners' Club. One question we see pretty regularly from new Prius owners is, "What does this weird button on my AC system do?" The button the new owners of Prius cars refer to is shown above.

Green cars like the Prius don't just have sleep aerodynamics and efficient engines. They go much farther and use special tires, special transmissions (if they even have one), and even special glass. One of the most significant ways that green cars can conserve fuel, after the big things are already done, is to manage energy used by the heating and cooling system in the vehicle. There are actually two relatively unusual buttons on the Heating and Air Conditioning control panel of the modern Prius. Let's look at both, starting with the one we indicate with the red arrow above.

The button that shows a large occupant getting treated air and then a small passenger with none refers to the Toyota Smart-flow climate control system. In a nutshell, what it does it direct full cooling or heating to just the driver. Obviously, this works best when you are alone in your Prius, or for times when you opt to torture your passenger (They may deserve it, who knows?). By only cooling or heating part of the cabin, your Prius saves energy, which translates to increased MPG. Not much, but in this green car, nothing goes to waste.

The second button, called the ECO Heat/Cool button, is just what it sounds like. When you use this button the car will manage the HVAC system to reduce energy use. Fan speeds are reduced, and AC compressor usage is also reduced. Be aware that in situations when the windshield is likely to fog inside the car, this should not be used.

For more detailed information on how the Prius' heat and AC system operate please check out the Prius Owners Manual. The information on this subject starts at page 512 and runs through page 525.

If you have any other questions on your Prius, feel free to post them below and we will do our best to answer them clearly and succinctly.

Subscribe to Torque News on YouTube.

Follow Torque News on YouTube, Twitter and Facebook.


Why should the heating settings knock down the mileage so noticeably? Settings like fan speed and temperature. Doesn't the heat come from the hot water in the engine and isn't the fan powered by the smaller battery in the back hatch? An air conditioner compressor I can understand would put a load on the engine but heat and a blower? When it's 10°F outside all I know is I want heat now with full blower, not on eco setting so I can gain a couple of miles per gallon when I'm already getting better mileage than anybody around me driving a non hybrid vehicle. Very curiously awaiting your answer.