How to use the automatic HVAC (FYI)

I found a very good source that explains nicely how to use the automatic HVAC efficient, here is the link, and below is the copied thread. Thought I share this bit of info with you guys:

"Since it seems like everyone in the world tries to use it a manual climate control, which it's terrible at, instead of automatic, which it's wonderful at, I thought I'd write a little guide

1) Choose the temperature you want the inside of the car to be. For most people this will fall somewhere between 67º and 72º. Personally, I'm most comfortable at 69º. The answer is NOT in the 50s or 90s (would you set your house thermostat to 91º? No, that would be ridiculous).

2) Set the temp display to your chosen 67-72º temperature.

3) Press "auto"

4) SET THE RED/BLUE DIAL TO THE WHITE LINE. AKA, it's purpose it not to be set to red in the summer and blue in the winter.

5) Press the recirc button until the left light is illuminated. That is the automatic position.

6) Done. Never touch it again, the car will take care of everything.




To clear up some misconceptions that seemingly everyone has:

1) setting the temp into the 50s will NOT make the car cooler any faster in the summer than leaving it on, say, 68º auto. The car will run the compressor and fan on full to achieve the target temp.

2) Similarly, setting the temp to 90º will not make the car get warm any faster in the winter. The car will crank the heat as soon as the heater core is generating enough heat for it to be beneficial to do so

3) The red/blue/white dial. 98% of the time, the correct position is the middle (white line) position. If you think the e46's climate control sucks (it doesn't), it's probably because you've messed with that dial. The purpose of the dial is to control the temp of the air blowing on your face beyond the climate control program. Good examples of when it can BRIEFLY be useful to tweak it: You just left the gym and you're overheated-- set to blue till comfortable, then back to white. Or, you just went trekking through the snow for days and need hot air directly on your hands and face-- set to red till comfortable, then back to white.

The default behavior of the dial is to blow cool air on your face while keeping the car at a comfortable (your chosen) temperature. Cool air is statistically proven to keep you more alert when driving, which is why this is done. On particularly cold mornings it will automatically blow warm out there till the cabin is warmed up, so there is no need to tweak it for that.

4) DO NOT TURN OFF THE AC COMPRESSOR. In the winter. In the rain. In the summer. In the fall. In the spring. In the winter, the AC compressor acts as a dehumidifier. Ever wonder why your windows fog up an other people's don't? It's because you turned off the AC compressor so your cabin is full of humidity. Same thing in the rain. It continually blows my mind how many people I see driving around in the snow/rain with their windows cracked and car fogged up, trying their hardest to see and not knowing that they are the cause of their own problems. Oh, and the AC compressor automatically disengages when your floor it, so it's not going to cost you any acceleration, either. Also, the AC compressor gets lubed through use, so not using it for long lengths of time will lead to premature failure. And, the car is less fuel efficient above 40 mph with the windows down and ac off than it is with the windows up and AC on, so you're not saving any gas, either.

5) The recirculate button. Three settings-- recirc, auto recirc, and no recirc. Auto recirc detect man made smells (chemicals, exhaust) and will automatically put the car in recirculate mode. 99% of the time, that's the mode my car is in. The exception is that it can't detect biological smells (e.g. rotting dead animal, skunks, etc). If you're going to be stuck next to one for a while, probably behooves you to put it on recirc for the duration.

6) unless you have specific reason to do so, don't direct where the air is flowing (as in, leave the lights on feet/face/dehumid on the left turned off). The car will move air about automatically as required.



So, to recap-- choose your temp, press auto, recirc in auto, snow flake on, dial to white, and stop touching it.

Used properly, the e46's climate control is pretty excellent. It can keep you comfortable year round without you ever having to touch it. In fact, the ONLY downside I can think of is there's no one touch off button.

Used manually, or trying to out smart it, it's a terrible system that constantly needs tweaking."

Ah ha! There is a Genie in there taking control of things after all. Thanks.

Thanks doru,

Re: "4) DO NOT TURN OFF THE AC COMPRESSOR". This is an important issue, but largely an issue in older cars made before 2003 or so.

This issue has been solved in modern cars made after 2005 or so.
In the modern car, once you hit the windshield defrost option, the car automatically turns on the AC compressor, if the ambient temp is above 25F or so.
This is basic Chemistry 101. When temp is above 25F, there is some moisture in the air that can fog the glass.
Once it is below 25F, most moisture in the air has condensed into snow/ice.

I know this is a feature in my 2007 Honda Odyssey van, when you hit the turn the knob toward "defrost windshield", the AC automatically runs, you cannot even turn the AC off.

So, if if you drive an older car and:
- It is raining
- It is 60F outside (cool) and you don't want to turn the AC on because it is cool, then turn up the heat a tiny bit, then turn on the AC to defog the glass.
I learned this the hard way many years ago!

very useful!

Very useful post.

My question is regarding #5 the recirculate button and how you feel it impacts moisture build up in vents. I had read years ago (I think in Roundel) that many people run into issues with a foul smell developing in HVAC system and this was due to moisture build up in the vents/tubes that feed the vents below the dash. The main cause of this moisture was the A/C staying in recirculate mode for extended periods of time, especially in hot weather with the system set in auto. One reason for auto mode being more of a problem than manual was that in order to try and reach the desired cabin temp in very hot weather the system will switch to recirc and stay there, BUT NOT give you the indication it is in recirculate mode. It is doing this b/c it is trying to achieve the desired cabin temp and with high ambient temps it has no choice, but to switch to recirculated air.

There were two suggested preventative measures. First don't run the a/c in recirc mode unless necessary and try no to do so for extended periods of time. Second when you are getting close to your destination run the fan on high with the a/c off for a few minutes to dry out the moisture from vents/tubes.

awesome post - i'm sure there are others like this one, but this is super useful to me.