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c_hunter 01-01-2005 08:20 PM

How The Dual-Zone Climate Control Works
The ACC system has three basic modes:

1) Automatic When you push the auto button, the systems does whatever it can to adjust the cabin temperature to meet the temperature(s) set by the user. In this mode, the only user controls are the L/R temperature knobs. In theory, you should be able to adjust the "comfort" level by tweaking the temperature knobs at any time -- if it gets too hot, drop the temp; if it gets too cold, increase the temp. Note that the operation of the system depends on the temperature difference between the current temperature and the desired temperature(s). With large differences, the fan will run at higher speeds and the system will choose more agressive venting modes. With small differences, the system will react to temperature inputs very gently.

2) Partial override From automatic mode, any control tweaked by the user other than the temperature control -- ie, fan speed, mode, AC on/off -- will force the system into a semi-automatic mode. In this mode, the system will continue to try and reach the set temperature(s) using whatever remaining options the user has not overridden. This is often confusing, and it may seem that the ACC system is posessed, as it appears to change something else every time you tweak a control. In reality, the system is just trying to reach or maintain the set temperatures with fewer and fewer ways to do it.

3) Manual If the user has tweaked all possible controls, the system will eventually be in full manual mode. Here, the user has complete control over the entire climate control system. In this mode, the temperature scale no longer relates to absolute temperatures in degrees. Rather, the range of 65-85 degrees maps to a general temperature scale from LOW to HIGH. Note that 65=LOW corresponds to no heat added (thus max cold) while 85=HIGH corresponds to the most heat added (max warm).

To get into manual mode on purpose, the best thing to do is press OFF, and then bring the system back online by pushing the mode, fan, or AC buttons. You may then tweak any of these settings as desired and the system will remain in full manual mode from there on out. This is more or less equivalent to a regular manual climate control system, except you have a fancy LED display!

Note that you can invoke a no-fan vent mode by starting from OFF, and then pushing the mode button to select face or bi-level ventilation. In this vent mode, the temperature display will not show and the temperature will remain at the previously set level (before OFF was pushed). So if you want a totally ambient vent, the procedure would be to set the dial to 65 (no heat), press OFF, and then press mode to select vent. Pretty complicated, eh? ACC systems don't have simple direct controls for something like this, unfortunately.

One thing that seems to bother people is that air conditioning (AC) runs almost all the time in AUTO mode. Well sort of. The AC compressor has a clutch, and it actually cycles on and off as needed (cars have been doing this for years). It cools the air in warm weather, and dehumidifies the air in cool weather (or when defrost is activated). All the while, the AC indicator remains lit. This simply indicates that AC can come on if needed, even though it may not be on full time. In extremely cold weather, the AC indicator will stay off until the engine warms up because it is too cold for the compressor to run. Once the engine warms up or the ambient temperature increases, the AC indicator may come on, again, to indicate that AC can activate if needed.

Another thing that bothers people is the fact that there is a world of difference between the temperature setting of 65 and 66. As discussed above, 65=LOW, or no heat added. So while 66 indicates a set temp of 66F in AUTO mode and it's the lowest setting for heat in the manual mode, 65 indicates "no heat". In AUTO mode, 65 actually translates to maximum cool (try it in the summer, it will frost your tootsies off). I really think Subaru should have labeled 65 as "LOW" (and 85 as "HIGH") similar to Acura.

Finally, many people complain that the system gets too hot or too cold while honing in to the set temperature in automatic mode. The solution for this is rather simple -- just reach over and turn the temperature knob(s) in the direction that will make you more comfortable. For instance, if you set the system to 75 in the winter and it's getting too warm, try cranking it down a few notches until you see the fan speed drop a level or two. What you are doing is telling the system "whoa" without having to fight with it; this really amounts to an impromptu calibration.

I hope this helps and saves people some grief. And for those of you who don't like the ACC at all, I respect your opinion -- I am just trying to alleviate some of the confusion that has been going around. I do agree that the system has flaws and eccentricities, and could be improved.


RoundBoy 01-01-2005 10:13 PM

A for effort..

but nobody will ever read it. They don't even read the manual... let alone search here.

Maybe if you group this with the elusive ILL5 error and the water in my intercooler threads.. it can get the recognition it needs

axis008 01-02-2005 03:40 AM

Thanks. I didn't read it either, but I will sticky it. If it becomes unstickied, it's because another moderator did it. :)

sduford 01-02-2005 07:14 AM

Excellent post Craig, hopefully it will help a few people.

However, it does highlight the fact that this is a poorly designed system that gets in the way rather then making your life easier as a well designed ACC system does.

I know, many of you disagree. What can I say, I must be whiny A-hole for wanting my car to work properly.

gtguy 01-02-2005 08:47 AM

Thanks, Craig. I'd already figured most of that out (men don't read no stinkin' manuals! :lol: ), which explains my satisfaction with the climate control setup.

I actually had a pretty cool experience the other night, driving home with a pizza. I wanted to keep me cool but the pizza warm. So I set the mode to "feet," and my temperature to 65, and the pizza's side (I had it on the floor) to 80. My tootsies were nice and cool, and the pizza box top was nice and warm. Man, that was weird. But with my WRX, I'd have to roast right along with the pizza. :lol:


DEI99662 01-02-2005 09:06 AM

Nice write up and I did read the whole thing...twice.:)

Ken S 01-02-2005 05:57 PM

Nice job as always, Craig.


emlevins 01-03-2005 04:57 AM

I read it too, Craig. Thanks.

mattm 01-03-2005 08:15 AM

I read it! Thanks, I wasn't aware of the difference between "partial override" and "manual" mode -- maybe that explains why sometimes I find the 66 setting to be OK, fairly cool air, while sometimes it seems too warm.


Kuth678 01-03-2005 03:29 PM

Hec I read it and I don't even own a legacy ;)

KTM 525 01-03-2005 04:38 PM

If you were to get in an ice cold car in the morning lets say it was 25 degrees all night and start the car set it to auto and 65 degrees it would not blow warm air (even after the engine is up to running temp) to heat the car to 65 degrees? Same senario but in the summer you get in the car after it has baked in the sun with the windows up all day in 100 degree heat. Start it up set it to auto and 85 degrees the AC would not come on to cool the car to 85 degrees?

c_hunter 01-03-2005 07:50 PM


Originally Posted by KTM 525
If you were to get in an ice cold car in the morning lets say it was 25 degrees all night and start the car set it to auto and 65 degrees it would not blow warm air (even after the engine is up to running temp) to heat the car to 65 degrees? Same senario but in the summer you get in the car after it has baked in the sun with the windows up all day in 100 degree heat. Start it up set it to auto and 85 degrees the AC would not come on to cool the car to 85 degrees?

You will still cool at 85, assuming 85 is lower than the cabin temperature. However, it won't be very cool! 85 is "Max heat".

In contrast, 65 is "no heat". It won't heat for beans, though it may have some carryover heating from the engine (the intakes are at the base of the windshield).


BobR 01-04-2005 08:09 PM

Great write up. It explains the demons in my system! Thanks.

Scooter 01-06-2005 07:54 PM

Clear, concise, extremely well-written - thanks, Craig! Have you ever thought of a career writing manuals?? I'm not really a fan of ACC systems in general, but I haven't found this one too bothersome. I do wish the fan speed control was a dial instead of buttons, though - it's kinda awkward to take your eyes off the wheel and find those buttons while reaching past the shifter.

c_hunter 01-06-2005 08:21 PM

Thanks for the kind words. Tell you what, on my previous 02 Outback with ACC, there was only ONE fan button. So you had to keep pushing it 1-2-3-4-1-2-etc to change the fan speed. That was a royal pain. They also had only one temp display -- it was either inside or outside but not both at the same time (yet there was plenty of empty space on the display for both). I liked my wife's 03 Forester, which had knobs for the ACC -- the fan knob was like a VCR jog dial -- just twist it once to change fan speed by an increment.


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