GenVibe - Community for Pontiac Vibe Enthusiasts

Ok...so we know that when the window defroster setting is chosen in the summer the A/C turns on, even though the A/C light doesn't turn on, to assist with the 'de-humidification' of the air to remove the 'fog'.In the winter when i chose the 'window defrost' setting but i have it set to full hot, so that i can melt ice on the windshield, i get the feeling the A/C is still turning on?!?! am i right? is this logical? do i have an option of changing this?

There is no option to change this that I know of. The reason that the compressor kicks on is that if it didn't, you would never run your A/C during the winter. THe compressor needs to run to circulate the freon in the system to keep the seals and hoses conditioned to reduce the fail rate. Older cars do not have this, and thus, higher failure rates for A/C components. So, when it does this, it is actually good for you.

Not to mention that when the vehicle is fogging up on the inside it is due to excessive moisture in the cabin. When the A/C compressor kicks in it dries the air. It aids in defrosting the vehicle's windows quicker than if it didn't operate that way.

The A/C would actually add moisture to the air, if i'm not mistaken, whereas the Heat is what dries it. This is why you need a humidifier in a home central heating system. I don't know the technical reasoning for why the A/C helps the defroster, but it does. I've disabled the automatic compressor turn-on in my Vibe, so it's only on when I tell it to, but it ALWAYS defrosts faster with the A/C on..

The way AC helps with defrost is exactly the same as how a dehumidifier works in you basement: The maximum percentage of water vapor that can be suspended in air is very temperature dependent (which is why dew forms as the air cools at night). A dehumidifier cools the air down close to freezing, causing much of the water to condense, then heats it back up, leaving the water behind and the air with a much lower relative humidity (drier). In a car, the dry air can better absorb the moisture as the ice melts/evaporates from the inside of the glass. Typically, the compressor does not operate below ~40 F., as freezing up the evaporator will block the airflow. (The same thing happens with a home dehumidifier: If the air is cool and really moist, the coils can get a frost build up and quit working.)

you all are correct and there is no way of bypassing that option, its standard on all GM vehicles now. Actually my 96 Sunfire GT did the same thing, on defrost the little green light saying the A/C was on even though the button would be off.

yep. always done that in just about every vehicle we've owned... except my tundra when i installed a rear defroster myself in the cap.

you mean so the windows don't fog up and freeze in the cold?

Quote, originally posted by silverawd26 »Yes... Because running it for a bit before you shut off for the night gets the moisture out.... And anti fog wipes work great also.Running the AC right before you shut off is a good way to reduce the humidity inside the vehicle, but it's also a good way to get mold growing in your AC system. Ever get into a car and a musty smell comes out of the vents? That's mold in the AC system....once it's there it's tough to get rid of the smell. And it's caused by running the AC right up to the time of shutting off the vehicle.Moldy AC is a common problem in Dakotas (my truck)...I've thankfully never had to deal with it because I shut off the AC for the last few minutes of driving. When I do that, yes I can immediately feel the humidity rise in the interior, but I'd much rather have humid air inside the truck rather than mold growing in my AC system. And opening a window for the last few minutes dissipates the humidity after shutting off the AC.Certain vehicles seem to be prone to this because of the design of the AC system...I can't say if Vibes are prone or not because I won't pick mine up till July. But for me, I'll continue to shut off my AC / defroster a few minutes before I shut down the vehicle to avoid mold.Just a different view is all...no flaming intended.

Yeah, there are ways to kill it...involves setting off a fogger in the interior with the recirculate turned on & AC running. The fogger is usually a combination air freshener / anti-baterial agent. It helps, but it leaves a smell I don't like (I've smelled them before...way too strong). And from what I've heard on Dakota boards, it usually doesn't kill the musty smell the first time.

It would have to be sprayed in the ducts or something, silver; the refrigerant couldn't directly affect mould as it's completely sealed and isolated from the outside air, like with the cooling system. (You cannot smell antifreeze unless there's a leak.)

Hey folks -- note that below (around) 3 deg C / 37 deg F, the a/c does NOT get activated when you use the defrost positions. The air is dry enough at these temperatures that it doesn't need to be de-humidified.At least - that's the way it's supposed to work. If it's cold and your a/c is coming on -- there's actually a problem. See your dealer.As for running the a/c system in the winter -- it's true that you should run it around once a month for a few minutes just to keep things working, but you'll have to remember to do that yourself. And to be honest, last winter I don't think I remembered and didn't run the a/c for some 4 months -- no problems this past summer though.

Yes the A/C light will come on even in the winter if you turn it onto defrost, but the compressor on the air conditioner will not turn on if the temperature is under 8 degrees celcius. so you will not burning extra gas and the A/C will not really be on. Right now i just have my A/C compressor unplugged so that even if it does get above 8 degress and i have it on defrost the compressor will not turn on till i plug it back in next summer

Quote, originally posted by PEDALS »Yes the A/C light will come on even in the winter if you turn it onto defrost, but the compressor on the air conditioner will not turn on if the temperature is under 8 degrees celcius. so you will not burning extra gas and the A/C will not really be on. Right now i just have my A/C compressor unplugged so that even if it does get above 8 degress and i have it on defrost the compressor will not turn on till i plug it back in next summerThe AC light doesn't come on in defrost modes any time of year...it's stealth...many people don't realize the AC is on in defrost modes unless the read it in the manual, or here.

Quote, originally posted by PEDALS »Yes the A/C light will come on even in the winter if you turn it onto defrost, but the compressor on the air conditioner will not turn on if the temperature is under 8 degrees celcius. so you will not burning extra gas and the A/C will not really be on. Right now i just have my A/C compressor unplugged so that even if it does get above 8 degress and i have it on defrost the compressor will not turn on till i plug it back in next summerare there any issues with unplugging the compressor (loss of pressure, etc.)? Where would you unplug it? Directly at the compressor?Interesting idea....

If you listen close you can hear it engage!!

Quote, originally posted by Atomb »are there any issues with unplugging the compressor (loss of pressure, etc.)? Where would you unplug it? Directly at the compressor?Interesting idea....There's a harness you can disconnect, but you have to pull out the climate control assembly from the dash...I really would advise against it, the compressor does make a difference...Anyway, should you decide to, here are instructions:http://home.comcast.net/~vibeowner/buzz.htmStep 6 notes the harness to unplug.

i don't think i'll go through all that...i did notice something yesterday...Temperature was 3C, and it was raining. I just started the car and it was in the 'hi-rev' mode (just under 2k rpm)....it slowly settled down to just under 1k rpm when i switched it to 'defrost'. the car was not moving at the time. As soon as i switched to defrost, the revs jumped up to about 1.5k rpm and i could hear the compressor kick in...then it stopped and the revs dropped back down to below 1k. So this could be the sensor detecting outside temperature and shutting off the compressor?Regardless, the air was hot, the windows defogged/deiced and it didn't sound like the compressor was on....i'll re-try again today....

all you have to do is find the compressor in your engine compartment and unplug the plug going to it... or even just go into the fuse box and unplug your a/c fuse and that should do the trick. i dont see a problem with unplugging the compressor the dealer has told me it is fine to do, and if not it's under full warranty for the next 5 years so they'll have to deal with it

if you unplug the compressor in the engine, you lose ALL A/C functionality...You're going to plug/unplug it every time you want to use the A/C?

yeah but up here in canada i'm not gonna need it till some time after may

Is the A/C supposed to kick in only on defrost or defrost/floor also?

I believe it does it on both

I thought so. What a silly waste of fuel. I prefer to use that setting most of the time. I don't like air blowing in my face. I will switch to floor only I guess.

I did what vibeowner has on his page, disconnected the plug from the AC controls, now no auto AC on defrost, but I can still do that if I choose to by hitting the AC button.