Heat or A/C?

Either way will work. There is no one way that is best for the car. I just set ac auto on some comfortable setting, and let it do its thing. In the early morning on a cold start, I may switch it off until the engine builds enough heat normally. Having a high heat setting will run the engine more if its cold to create the heat. The main thing is, make yourself comfortable, the car will figure the rest out. If you just want ambient outside air, go to the climate screen, switch AC off, and select the fan speed and temp you want (I use LO for most California mornings). Its all pretty much the same, regardless, depending on your temp setting. It sounds more comfusing than it really is.

 

I use auto A/C year round with the AC selected. The compressor is electrically driven and will only come on when necessary. It also keeps the windows from fogging. Just use the temperature control to set your comfort level and let the auto system work as designed.

 

Keep in mind that in the Prius "A/C" really does mean "air conditioning" and not "air cooling". If you turn on AUTO it decides which outlets to open and how fast to run the fan; all you need do is set the temperature. Beyond that you can manually set/override as few or as many things as you like.