Heater/AC questions.....2007 Prius.

I also live in upstate/western NY.

The best option I've found is to just turn on AUTO, Turn OFF AC and set the temperature you want, with the following adjustments:

-If the windows are just slightly fogging up then turn the AC back on.

-If you really need defrosting, then use the defrost setting.

As far as letting in outside air, you definitely want that. If you try heating the car in the winter without taking in outside air you will very quickly fog up all of the windows.

Levi

 

I leave mine in Auto AC year round. The AC compressor is electrically driven and will only come on when conditions warrant. Just adjust your temperature to be comfortable and don't make a science project out of the climate control system. It's smarter than most of us.

 

Yeah, on a manually adjusted car you would want to leave it set to outside air during the winter and recirculate when using the AC in the summer. I just Googled it and came up with the reason:
"job #1 is keep a good flow of air coming in from the outside. In fact, the colder it is outside the drier that air is, so the more beneficial it is to compensate for your breathing."
The car does heat faster by using recirculate but the moisture builds up and then you can't see.

I doubt you'd feel cold air blowing in when bringing in outside air. I don't normally leave mine on the climate screen so I don't even know when it's bringing in outside or recirculating. I definitely have left the vent to outside air on every car I've had in temps down to -40F and the cars still blow warm air. (with the exception of my 03' Prius with a blown headgasket where it couldn't keep enough coolant in to flow through the heater core)
The only thing I've noticed is that there are times when I set the temp to like 65 which feels plenty warm normally, but then under certain conditions it's still blowing 65 degree air(because the car is already at 65) and then it starts FEELING cold due to the moving air hitting you. BUt it's easy enough to just turn the temp up a few degrees and feel warm again.

I'm down in Avoca, near the I86/390 split.

Levi

 

The system is smart, but it still uses more fuel(albeit not a lot) when the AC is on and they haven't gotten it to really know whether it needs to be on or not.
I don't know what it's exact rules are but in the winter around here it doesn't need to be on unless the windows are fogging, so that's the only time I turn it on. (and it will run whether the windows are fogged or not otherwise)

Levi

 

I didn't realize that you have an '03. Maybe the system is different in the Gen I from the Gen II.

 

It does this to reduce interior humidity and reduce window fogging. The heater will work harder to maintain the set temperature. If you manually go to recirculate the "Auto" indicator goes out but the other functions (temperature control, etc.) remain in Auto. I do this a lot during defrost to avoid sucking in outside bus exhaust and whatnot. When the outside air seems clean I manually set it to outside to reduce the humidity.

 

Recirc is a really bad idea in the winter. If you get the car all warm and toasty but humid, then the next morning when you get in the car you'll be spending a lot of time scraping the inside of the windows. Even without recirc this can be a problem if you're bringing in too much moisture (boots, breathing...) so sometimes when I'm getting close to my destination (1-200 metres) I'll open a window to give me some nice dry air to leave in the car as it cools. Another option, if you're not expecting snow, is to leave a window open a couple cm to let warm/moist air out.

 

I traded the 03 for an 04 which I was referring to.

Definitely different systems. The 03' only has auto temp/fan speed. Recirc, ac and vent control are all manual.

No matter what car you're in I'm not aware of any without a recirc control, nor any that is not likely to fog the windows with recirc on in the winter while trying to heat...