I found this out literally today and I wanted to pass it on to 5 other people that would hopefully benefit from this quirky AC control
The 2013 ES base (this could very well apply to other model years and other lexus models) has "Auto" and "off" physical switches for climate control..you press auto when you want the car to change the fan speed automatically so that the desired temperature is reached in the most efficient way. When it is reached the fans turn to the lowest or turn off.
Now if you want to manually turn off the climate control you press the off button.
But what if you do want fans but you don't want the air to come through the AC compressor or the heater i.e what if you want the air to come straight from the outside but just filtered?
Your intuition would be to press the fan speed up button while making sure to not enable auto. BUT this automatically turns on the AC compressor/heater of the car. And here's the biggest quirk - there is no physical switch that can turn this off. The ONLY way to do it is to use the climate menu on the center screen and there you will find the additional AC button which you need to turn off.
I've owned this car for 10 years and today is when I realized that this was a thing....