Automatic climate control?

August 28, 2007 7:25 AM

First car with automatic climate control. How does it work?

About a month ago, I bought a 2008 Subaru Forester. It's the first car I've owned that includes automatic climate control, and the owner's manual isn't particularly clear on how it works. I've been running it in "semi-automatic" mode, giving me greater control over settings, and since it's been hot lately and most of my driving is done during the day, I've almost always kept the temperature at its lowest setting (65F). However, now that's it's starting to cool down outside (I live in Colorado), I've been setting the temperature a bit higher (~70F) and have noticed that, when I do, the air flowing from the vents is much warmer than I'd expect.

While driving to work this morning, however, things got more complicated. I set the temperature to 70F only to have the heat itself kick in. The outside temperature at the time was 62F, but I was driving into direct morning sun, so it was warm enough inside the car that I wanted at least some cooling - not heat. Out of curiosity, I set the temperature even higher (~85F), and the air coming from the vents continued to increase in temperature. So, it wasn't like I was getting full heat at 70F. I continued to drive for awhile with the temperature set at 70F, and while the temperature of the air seemed to fluctuate some (there was a hint of cooling every so often), it remained warm until I got to the office.

So, my question... is this how automatic climate control systems work? Since the outside temperature at the time was 62F and the car had been sitting outside all night, I can only assume the ambient temperature of the cabin was no higher than 70F. By setting the temperature of the climate control to 75F, would it compensate by blowing hot air in order to bring the temperature up as quickly as possible?

For what it's worth, the owner's manual seemed to indicate that keeping the temperature at its lowest setting (65F) would result in maximum cooling, no matter what, and since that's where I've been keeping it until now, that would explain why I'm just now noticing this quirk... assuming it is a quirk, that is, and not a problem that needs servicing.

posted by jal0021 to travel & transportation (7 comments total)

What did you expect to happen? I'm a bit unclear on what you think the quirk is.
posted by bonaldi at 7:55 AM on August 28, 2007

Does it show you the interior temperature? Because that's what it should be using to run the climate control, not the exterior temperature.
posted by smackfu at 8:08 AM on August 28, 2007

No, the interior temperature isn't displayed.

And Bonaldi, if I gradually increased the temperature setting, I would expect the temperature of the air to gradually moderate... not for it to immediately start blowing hot air. Basically, I'm trying to figure out if this is normal behavior or not.
posted by jal0021 at 8:17 AM on August 28, 2007

The automatic climate control acts pretty similarly in my 05 Mazda 6, so I think it's just the way the thing works. I have been adjusting manually since I find it's easier.

I, too, might just not understand the thing, though. I really haven't given it much thought since originally being confounded by it.
posted by boreddusty at 8:47 AM on August 28, 2007

My 2005 Legacy has the dual zone climate control. It is a weird and frustrating beastie. It is badly mechanized and it reacts both too rapidly and with too little damping.

Here is how it works, beginning from a push on the 'auto' button.

In 'auto' the control will attempt by many means to make the interior air temperature match what's set on the control, except if it is set at 65 - which means it will cool as much as possible - or 85, which means it will heat as much as possible. If you actuate the fan control, the A/C button or the mode button the automatic strategy will continue to try to reach the designated temperature while respecting the setting on the control you actuated (and the 'auto' indicator will go out).

The ACC takes account of solar load via the dime-sized black plastic gizzfratchet on the dash, and it measures the interior air temperature with a little air pump whose intake is - on my Legacy - near the driver's right knee. The temperature of that air is not displayed.
posted by jet_silver at 8:58 AM on August 28, 2007

On full automatic mode, you tell it what temperature you want it to be, and it does whatever it deems appropriate to make the interior of the car that temperature.

If it's 62 and you set it at 70, it will heat the car to 70 degrees.

If it's 85 and you set it at 70, it will cool the car to 70 degrees.

If it's 85 and you set it at 65, but you really only want it to be cooled to 70, you'll be frustrated and fiddling with the fan all the time.

The temperature you set it at is not the temperature of the air coming out of the vents, it's the target temperature that the system is working to achieve in the car.

If you were to just leave it at a temperature that you like, and put it on automatic, the fan would stop all by itself when it got to that temperature, and you wouldn't have to fiddle with it.

I've had auto climate control in several cars and some have worked perfectly (Lincoln) while others have been dismal (Fiat/Saab joint venture thinggy) (Yeah, who would have thought that a joint venture between Fiat and Saab would have unreliable electronics?)
posted by The World Famous at 9:42 AM on August 28, 2007

It sounds like we have the same system, jet_silver (although mine is only single zone), and from your description of how it works, my guess as to what happened this morning is that the temperature control was set to auto, yet the fan was set to manual. Thus, that's why I got the blast furnace effect once the heat kicked on. Had I had the fan set to auto, I suspect it would have cut back enough to where the heat wouldn't have been all that noticeable.

I guess I'll have to play around with the various settings as the weather changes... the fact that you can set the various features to either auto or manual independent of each other makes for a variety of combinations. No wonder the owner's manual suggests setting everything to "auto" and being done with it.
posted by jal0021 at 12:09 PM on August 28, 2007