Ok, weird little issue here.

When I hit the "auto" climate control button, the AC turns on and that light never goes out (even if I crank it to 80 and it's 30 out).

I don't get it. What is automatic if I have to push auto, then turn off the AC. If I hit auto again, the AC light pops back on. I understand it for the defroster, but what the heck is going on with the climate control that when it is 30 outside and not much warmer in my garaged car, if I turn on the climate control by hitting the dual auto, the AC always turns on?

This happened all summer, but it was hot this summer. Why is this happening? It's making me a little nuts...

 

I have the same issue. I read on another blog that the AC runs to control moisture and not as a cooling function. So the windows don't fog up. I don't know if this is true or not and would like to hear from someone that knows more on the subject.

 

Right, which is why when the defroster is on, I get it.
But when it is freezing outside, shouldn't the AC not be on? I don't want the AIR CONDITIONING on when it is 34 degrees out. I want heat.

 

I have no idea why it's on, i have been wondering the same thing for a while now..... I haven't messed with my settings for a while and noticed it stays off now when I start the car. I could have sworn that the AC came on without the defroster though. I have to go mess with this now.

 

The AC does come on with the defroster, which makes sense.
It stays off if you don't mess with the climate control. But if you turn off climate control and turn it back on, the AC kicks on.

My dad says this happens in his Corvette too (and that it annoys him), but offered an explanation. Apparently, he believes it is to remove humidity. Which raises the question: why does it stay on if I don't shut it off. The AC shouldn't be on all the time if I want heat....

 

That's a good explanation. I was messing with it earlier and when I turned the defroster off the AC stayed on. I am sure it's working the way it is supposed to and it just annoys me.

 

I see we have a misconception here.

Under the conditions we have in winter, the AC IS NOT cooling the car. The temp in the car is whatever we set the controls for. The AC during cold weather is simply removing excess moisture from the air, and this is a very important safety function.

I seem to recall this came under under federal safety guidelines back in the 1990s, and it certainly should be.

We can run without the AC in summer if we wish, but we should NOT be running the car in winter with the AC off, unless we live in Arizona or somewhere where there is zero moisture in the air.

 

Thanks! I never knew that. I am glad to know it is functioning as it was designed to.

 

Safety? Any chance you have any documentation or can provide a link that discusses this?
I'm not calling you a liar, I just think you might be misunderstanding something. If it was a safety factor, then why wouldn't it be the same on a manual climate control? My last car had manual climate and the manual made no mention of ever running the AC in the winter unless the defroster was on.
I'd like to learn more about the subject, so any links or documentation would be very much appreciated.

Thanks!

 

I think it's Nissan's way of doing their part to help with global warming.

 

I understand the ac comes on in the winter because the compressure would freze up from not being used during winter. it is to keep the ac working but in order for cold air from a ac the temp outside has to be at least 50 and above older cars had ac compressure come on only with defrost I believe they now have ac come on with defrost and automatic just as preventive brake down on the ac during winter.with automatic u can shut the ac compressure off not to cycle but in defrost I believe u cant stop the compressure from cycling on and off . hope this helps

 

Jeff - I probably could have had the references at hand ten years ago, but this has been standard on the Maxima (and most newer vehicles) for so long that I just assumed most folks were aware by now. I will look around for a reference when I have more time. In the meantime, what Milliam M Murphy says in the post above is very pertinent.

The key to remember here is that the term AC means 'Air Conditioning', NOT 'Air Cooling.' The AC light is the instrumentation telling us the compressor is running. It is NOT telling us that the unit is putting out cold air.

If the ambient air is above a certain temp, all the compressor is doing is removing moisture from the air. And as williammmurphy said above, this is helping the AC system maintain itself through the long winter, when many folks, not knowing the unit must be frequently used in order to function correctly, would never turn the AC on.

 

This takes me to a few other questions then...
If the compressor should be turned on during the winter, why is this not part of every owners manual on every car as a maintenance item? I had an 05 Accord. The AC went on precisely zero times during any winter I owned it and never once had any problem.
Next up - if it is just supposed to run a little while, why won't it shut off after a while? I didn't futz with it once today and was on the road for a total of over an hour - twice- and it never shut off on its own.
And then this - what is the magical temp the car uses to determine if the compressor should come on? Because last week, it was in the 30's and the thing turned on every time I hit the auto button.
Further - maybe mine is broken, because even with the outside temp in the mid 30's and the temp set to 70, all I got was cold air.
Finally - won't running a compressor every day burn it out faster than only running it when it is needed? My home AC doesn't go on once in the winter and doesn't seem to have a problem....
I know what I wrote just came off as smart alecky - not messing with you, just in a rare mood. I do appreciate the responses and am just having some fun with my questions and responses....

 

jeff - The AC in your home does not come on during the winter because it has only one mode - cooling - and we don't want cooling in the winter.

Your home does NOT need dehumidifying in the winter. In fact, any good home HVAC system actually has a humidifier which ADDS moisture during the heating season because home heating systems take most of the moisture out of the air, leaving very dry air which causes uncomfortably dry nasal passages and sparks every time we touch metal or drag our feet on a carpet.

The heater in a car works in an entirely different manner, using engine heat, and does NOT remove the humidity from the car. But, because of the critical importance of being able to see clearly out of the car, humidity MUST be removed from the car to prevent window fogging. The AC unit in the car does this in summer while cooling the air, and in winter by removing the moisture without cooling the air.

Of course we must set the temp high enough to prevent the AC unit from cooling the air as it removes the moisture, else the unit will go into cooling mode. In winter, this setting must be much higher than 70 in order to keep the unit from cooling. By experimenting, I can always find the magic spot at which the air is not cold, and the car is not being overheated.

Although the owner's manual does not emphasize this, and sometimes does not even address this, I have known since my first car with AC over fifty years ago that we are supposed to run the unit occasionally during the cold season in order to prevent the seals from drying and cracking, etc, etc, which can shorten the life of the unit and cause other problems.

This was emphasized a lot when AC units were new in cars, but as the AC systems improved over the years, the emphasis on occasional use during the cold season gradually faded.

You may not have had trouble because of not running your AC during the winter, but that is an example of one. That does not mean that all drivers will be just as lucky. In truth, the AC units in cars these days are very dependable, and are built to last the useful life of the car. I have owned nothing but Maximas since October 1984, and have never had a problem with my AC compressor.

The AC unit does not shut off, as there is almost continous moisture in the car, eminating from our bodies and from our breath. When this moist air comes in contact with the inside of the windows, it condenses there because the surface of the windows (which are cooled by the air outside the car) is much colder than the air inside the car. Having the AC shut off at some point would simply mean the mist-caused accident will be later in the trip instead of earlier.

The primary purpose of having the unit run most of the time in winter is safety. Window fogging may not be common in some areas, but on cold mornings, I almost always eventually see fog inside my car windows if I don't have my AC system on.

 

Just blew my mind. I cant wait to be the cool kid in the office when/iF this topic comes up lol thank you

 

I did the research to see how right you are and, as it turns out, you are very right.
I appreciate two things most of all:
1) Your willingness to share information, and;
2) Your ability to resist being a huge jerk.
I was an active member on a Honda forum and while some were willing and eager to share information, others played "hide the ball" and would respond to every query with "search is your friend". Worse yet, when I would challenge people to explain because I was clueless or simply disagreed, things sometimes got nasty.
This forum has been different (so far) and I'm the sort of guy who likes to thank people for being kind.
So thanks!

 

Good thread happening here. And from what I've seen lightonthehill's responses have always been on the money. If he chimes in, you can usually bet there's experience behind his reasoning and suggestion. Long story made short, the AC is about air CONDITIONING, not necessarily air COOLING. Good stuff.

 

Best explanation ever!