I was very confused by this also when I got my '05 Prius. Not only was the button confusing, but the text on the heading of the Climate Screen. The fact that when I pushed the "Climate" button, the screen heading read "Air Conditioning" was confusing, I eventually assumed that Toyota meant "air conditioning" not to mean "cooling the air" but, "conditioning" it to hot or cold depending on settings.

I guess when I hit the climate button, I would have expected a screen heading of "Climate control". Seeing "air conditioning" made me try to hunt for a screen for "heat".

2005 Salsa Red Prius w/Package #4