Can someone explain how this works please? When I hit auto sometimes the a/c lights up, sometimes it doesn't. I want to know what makes it come on so I can prevent it. Is it outside temp?...which doesn't seem likely. Is it the previous setting?...which isn't happening. I have my temp set to 80' and when I get in the car and hit auto, the a/c comes on 85% of the time.

Everytime i hit my auto climate control it goes to a/c. Doesn't matter what i do it always goes to a/c

When you have the climate control on auto it defaults to trying to make you comfortable. A lot of thermodynamic magic happens when the A/C is on to rid the cabin air of moisture. In the summer the air is humid, so the A/C brings the air moisture down to a comfortable level. In the same line, in the winter the cabin air is most probably more moist than the outside air. The point here is that this air hits the cold glass and you have frost on your windows. A/C programming wants to prevent that from happening.(That's why even when your climate control is off and you hit the window defroster, the A/C kicks in)

So, yes in a basic system the A/C kind of depends on temperature (internal and external)... and it will most likely come on in the winter and summer, as long as you have it on auto.

Couple of blurbs out of the FSMs on Auto
ATC-30
AUTO SWITCH
• The compressor, intake doors, air mix doors, mode doors and blower speed are automatically controlled so
that the in-vehicle temperature will reach, and be maintained at the set temperature selected by the operator.
• When pressing AUTO switch, air inlet, air outlet, fan speed, and discharge air temperature are automatically
controlled.

Also to perform self diagnosis if you suspect of an issue as indicated your AC light automatically turns off while still in Auto. Mine doesn't regardless of temps although mine is an 06. Check out ATC page 50 and beyond to try the self diagnosis without a scan tool.

I have an 09 M, but the system works thew same way my 07 did. The few times I have the car in the north where heat is needed, here is what happens:

The temp in my car is always set to 70 on my side, and 75 on Fetucini's side. In cold temps, the A/C will activate each time the car is in AUTO mode. I simply switch off the A/C button and the car reverts to heat. I don't know why (aside from what was stated above) the car doesn't "know" that heat is needed when the outside temp is much lower than the temp I set inside my car, but it always turns the A/C on and to get heat, I have to switch the A/C off. Far as I know, that is normal.

Even in my 1968 Fleetwood, you set the temp dial to what you want, and the car switches from heat to A/C all by itself based on the temp difference. When it switches itself to heat mode, you can hear the floor vents and windscreen vents opening and the dash vents close. It's truly automatic temp control in the 47 year old Fleetwood.

Larz's observations are also true with my '06 M45.
Plus, if you're in recirculation vs fresh air mode, the A/C kicks on too. You can't turn off the A/C and have the system stay in recirculation mode for some reason... prolly for some of the same reasons that Larz stated above.

Found this interesting from the owner's manual (might be one of those "wow, didn't know my car could do that factoids" - a separate thread)

From Section 4-27:
In the AUTO mode, the intake air will be controlled automatically.
To manually control the intake air, push the intake air control button.
To return to the automatic control mode, push the intake air control button for about 2 seconds.
The indicator lights (both air recirculation and outside air circulation sides) will flash twice,
and then the intake air will be controlled automatically.

From Section 4-26:
Automatic Operation
Cooling and/or dehumidified heating (auto)

when you want just heat ALONE, the owner's guide states to manually press the A/C button to turn it off.
it also states in heat only mode:
Do not set the temperature lower than the outside air temperature.
Otherwise the system may not work properly. (you want heat, but you set the temperature inside the cabin to be cooler than it is outside....car prolly thinks you've gone nuts...lol)

(so it makes sense that the A/C unit light is going to be on if you hit auto regardless of the ambient temperature, if it's hot outside, the engineers at Infiniti want you to be cooler in the cabin, so A/C on = lower humidity and cooler temp, if it's cool outside, the engineers want your heat apparently dehumidified)

Craig

This post feels like it's loaded with misinformation, so I'm just going to drop this in here (post is from 2010, it needs readers, not necromancers):
defrost-is-hard-to-get-right-t458805.html

I highly recommend the OP and everyone else who thinks they need to turn the A/C off when Auto is on read the entire thread and then consider going to a mechanic if they seriously can't get heat with the A/C on (maybe it takes a fully warmed up engine vs just a little heat from the engine, and maybe it is convenient not to wait for that, but turning off the A/C shouldn't be necessary beyond that).

Also, since it may not be mentioned in that thread or this forum, I believe the other reason the A/C light stays on is because an A/C that is always run is less likely to seize up, so those living in places that have a winter may get longer compressor life by leaving the A/C button alone vs turning it off all winter. I believe I learned this reason first on another forum with another car where the A/C light meant Air Conditioner vs Air Compressor (even per the manual).

Good points there dustin. Keeping the compressor circulating even in auto mode ensures the refrigerant oil is circulated throughout the system even over the winter months. The O rings and the piston needs this oil moving so they don't harden and crack especially on the high pressure side.

The00Dustin wrote:This post feels like it's loaded with misinformation... but turning off the A/C shouldn't be necessary... an A/C that is always run is less likely to seize up....

Good points on keeping the compressor healthy.

I think the biggest misinformation, or rather misconception, is that A/C is the opposite of heating. I usually explain to people that A/C is just that - air conditioning aka moisture control. And that happens at various temperatures.

The00Dustin wrote:This post feels like it's loaded with misinformation, so I'm just going to drop this in here (post is from 2010, it needs readers, not necromancers):
defrost-is-hard-to-get-right-t458805.html

I highly recommend the OP and everyone else who thinks they need to turn the A/C off when Auto is on read the entire thread and then consider going to a mechanic if they seriously can't get heat with the A/C on (maybe it takes a fully warmed up engine vs just a little heat from the engine, and maybe it is convenient not to wait for that, but turning off the A/C shouldn't be necessary beyond that).

Also, since it may not be mentioned in that thread or this forum, I believe the other reason the A/C light stays on is because an A/C that is always run is less likely to seize up.

I don't get what you're on about with necromancers. I see no wizardry or witchcraft here. That said, I sincerely thank you for clearing up the bit about switching the A/C button to OFF. My 2009 manual instructs me to leave the A/C switched ON for dehumidified heating, and to switch it OFF for heat only (no dehumidifier). Apparently, either way is not a problem for the car, but it DOES mention that heating with the A/C switched to OFF can result in fog collecting on the interior glass surfaces. I reckon that leaving the A/C switched to ON is the best method and also beneficial to the life span of the compressor, so I shall leave the A/C button switched ON going forward..

Larz wrote:I don't get what you're on about with necromancers. I see no wizardry or witchcraft here.

On the off chance that you're serious here (and for anyone who might need to know even if you're joking): a thread from years ago is considered a "dead thread" in most forums. Posting in such a thread "brings it back to life" and is referred to as "necro posting" (or something like that). This is usually frowned upon, and while I don't understand why it is frowned upon (I can see how it is pointless in many circumstances, but not really harmful), the comment on necromancers vs readers was a friendly reminder to let the thread I linked to rest in peace.

Dustin: Please forgive if it seemed I was trying to correct your use of words. I was sure you knew what you typed, I honestly didn't get the meaning of it's use here. This is the only forum I have spent time in, so please forgive my ignorance for not knowing about reincarnation of old threads.
Also, thanks again for prompting myself and others to actually read our manuals. In cold weather, I need to switch my thermostats in the house from the A/C setting to the HEAT setting and blindly assumed it was the same for this car without searching old threads in here or reading my car manual. All is good and I apologise if my post was taken as critical in any way.

I don't mind people bumping an old thread to ask a question...but often times old threads get bumped with something that was useless...pushing real/current issues down the list. This is why forums frown upon it. I let it slide if it's a meaningful post.

For anyone reading (especially lurkers), what I don't really let slide is posts that have been covered 10000x times. Had a member in another part of the forum asking the most basic stuff...search first please.

Anyway, carry on .

I came across a video suggestion on youtube, that reminded me of this thread I had contributed to. This is not to beat up a dead horse, it's just a video with cool analogies for people who learn better that way:

Thats great info, especially the shaving cream. I wonder however, the film that the cream will leave on the window, especially heating up over time. Also, I've always been told never to turn the heater on full right away be ause you'll damage it, and I think that is the reaon when set to auto this heater slowly comes on as the car heats up.

I am wary of the residue on the windshield as well. I haven't had to use any products as I usually just budget for around a minute or 2 for this fine automatic system to clear my windshield. If there's ice on the outside, I just wait for 5 minutes and the wipers handle the job easily (since I took my first thermodynamics class I vowed to never have to scrape ice ever again - but I clear thick snow for safety)
As for using the heater at its maximum I don't see much of an issue except discomfort. My understanding of the heat intake in a car is just how much heat exchange is allowed from the coolant through the heater core into the cabin. So, regardless of what temperature you set it to, the time taken to achieve your temp setting depends on the engine coming to temperature. If this were a resistance heater then, maybe I see max temp relating to high current and maybe more wear?
...but I'm going to think about this a little deeper during the day.

EDIT: I'd say yes, in auto the blower is slowly ramped up for comfort. The makers understood that depending on coolant temperature, there is no use blowing air at maximum speed at anything other than the windshield.

The best A/C compressor ever engineered in the history of mobile transportation was the old Delco A-6 unit. I smile anytime I still see one in operation. Larz can appreciate it every time he opens up the hood on his 68' Fleetwood!

The A-6 had a sump molded into the lower end of the case shell. When the A/C shut down, oil in the compressor migrated to the sump in the case....effectively never leaving the body of the compressor! Upon start up, the oil only had to be pushed from the sump back into the upper reaches of the case via the swash plates...!

Swash plates & sumps are long gone...now oil in a compressor eventually migrates into the condensor upon shutdown of the compressor. Not a problem with periodic usage, but long term dormancy is like starting your car up after a long sleep....a good portion of the oil has left the upper end of the engine, has to get pumped back up to the cylinders, lifters, rockers, etc. So, like an engine, a dormant A/C compressor that is initially started is oil starved until that oil can get back into the unit!

On my 06 M35, I leave the auto setting on for a few minutes just to get the oil circulating, then I shut it down if I do not need the compressor afterwards. As I am in NY, the compressor pretty much gets a workout during all four seasons anyway, so I feel using this discrection causes no harm. If I rarely used the compressor however, I would want to run it whenever I could to keep it well lubed, as Dustin points out, to ensure longevity of the unit!

EdBwoy wrote:.......My understanding of the heat intake in a car is just how much heat exchange is allowed from the coolant through the heater core into the cabin. So, regardless of what temperature you set it to, the time taken to achieve your temp setting depends on the engine coming to temperature. If this were a resistance heater then, maybe I see max temp relating to high current and maybe more wear?
...but I'm going to think about this a little deeper during the day.

EDIT: I'd say yes, in auto the blower is slowly ramped up for comfort. The makers understood that depending on coolant temperature, there is no use blowing air at maximum speed at anything other than the windshield.

Agreed!

Did you know at one time a car manufacturer addressed this very issue?
Back in the early/mid 70's FoMoCo (Ford) came out with an electrically heated front windshield that ran off of a separate hi-amp alternator attached to the engine pulley system. You actually had 2 alternators under the hood, one solely dedicated to front windshield defrost! I worked at Lincoln-Mercury at the time, it was a rare option, but I did see a few on their upper tier models (Marquis, Continentals, T-Birds, etc.)

To digress if my may (begging Ily'a discretion) The subject of pre-heat driveability is current in automotive news, one domestic in particular!
A few years ago, an auto manufaturer offered a pre washer fluid heater as an option. It was prone to failure, a recall ensued whereby the dealership disconnected the feature, and allocated a refund for the option!

more recently, the same manufacturer had an automatic rear window defrost feature on the remote start keyfob option. That was recalled and disconnected due to the system unable to regulate the time of heat applied to the window!

So...it seems manufacturers do understand convection weakness vs resistance advantages in cold/freezing start driveability, but it seems other than the now standard electric rear window defroster introduced in the very early 70's or so, front windshield defrost/de-ice and cabin warm up is basically the same now as it is on Larz's 68' Fleetwood! The few attempts I noted above to change this have failed to date!

In 1996 I bought a new Impala SS with an engine coolant heater. What a world of difference in cold start/freezing warm up! I wanted that for my 06 M, not available as an option at the time.

TDot wrote:Also, I've always been told never to turn the heater on full right away be ause you'll damage it, and I think that is the reaon when set to auto this heater slowly comes on as the car heats up.

Hmmm ... I interpreted the slow increase in fan speed, etc., to the desire to prevent blowing freezing cold air in your face at high speed. So they let things and the heater warm up a bit before the air kicks in. Makes for a more comfortable experience for the people in the car.

Z