What does "Max A/C" do?

[The Critic]

Originally Posted By: brianl703
You may well end up with fogged windows if you try this.


According to Toyota's Scheduled Maintenance Guide, if you get fogged windows while the HVAC is operating in that mode, the cabin air filter may need to be replaced.

Originally Posted By: Eddie
RtexasF. A rude comment for sure. The two vehicles I am familar with that have an AC MAX option, set the compressor to run full time or more than usual and in the REC mode. In add ition, the fan speed runs at full output also.


What do you drive?

 

[brianl703]

Originally Posted By: The Critic

According to Toyota's Scheduled Maintenance Guide, if you get fogged windows while the HVAC is operating in that mode, the cabin air filter may need to be replaced.


If that's the case, then it's pulling some outside air in while it's in RECIRC.

 

[brianl703]

Originally Posted By: Eddie
RtexasF. A rude comment for sure. The two vehicles I am familar with that have an AC MAX option, set the compressor to run full time or more than usual and in the REC mode. In add ition, the fan speed runs at full output also.


You mentioned in an earlier post that using MAX AC too much results in the evaporator freezing up.

If the evaporator freezes up because it's set to MAX AC, something is wrong.

An evaporator should NEVER freeze up. If your vehicles really do run the compressor full-time in MAX AC and it never cycles, then that's why it freezes up. Suggest checking the clutch cycling switch for proper operation.

 

[jim302]

Originally Posted By: Eddie
MAX does not allow the compressor to cycle and keeps the rec locked. Good for cooling down the car but, should not be used continually because the evaporator can freeze up.


This isn't the case, since a frozen evaporator does not cool well. If you've ever had your defrost timer fail in your home refrigerator or had a refrigerant leak freeze your evaporator in your home A/C unit, you'll know exactly what I mean. Further, continued operation with a completely frozen evaporator is bad for the compressor.

I believe the MAX A/C option is there to simply reduce customer complaints and unnecessary trips for service (especially under warranty). When someone is sitting in heavy traffic in very hot weather, and the A/C can't keep up whey trying to cool that hot outside air, they are hoping the driver will notice the MAX setting and use that.

On every car I've ever been in that has this feature, MAX A/C simply forces recirculate and forces air to come out of the upper vents. You can't turn off recirculate in MAX A/C mode. It still allows for adjustment of the fan speed. There is usually better air flow in recirculate at any fan speed. This seems to be related to the design of the duct work, since the fan speed doesn't change.

 

[Thermo1223]

Little question BIG discussion it seems. Well I think we are all trying to describe our own cars which is half the problem. Excuse me to be analytical for a moment about most of the cars I've driven over the years.

So lets analyze the A/C system shall we.

First 1991 Caprice:

Manual fan control and suggestive vent options. No recir. button, no A/C button. Max A/C meant compressor on, recir on. Normal & B/L meant A/C w/ no recir. It also had defroster linked A/C meaning the A/C was on when set to defrost(unless to cold of course). Standard compressor as well, it cycled no matter what.

1993 Saturn Sl1:

Manual Fan control, A/C, & recirc. Also Defroster linked A/C, A/C could be used in any way as well as recirc. except for defrost. It was disabled if memory serves. This meant the only time use of outside air was forced was in defrost. Standard compressor as well, cycled.

2000ish SL2:

Same as above but I know for sure newer SL's didn't illuminate the A/C button in defrost even when it was on(since defrost enables it by default). I am unsure about the older models.

2001 Hyundai Accent:

Manual fan, A/C, & recirc. control with a special note to the mechanical recirc. lever. Similar to Saturn with A/C enabled in defrost but the button light being lit when so. I note by the defrost settings to use outside air to prevent fogging. You could technically use recirc. on this car whenever you pleased.

2000 VW Jetta:

My old car which I miss dearly, Manual fan, A/C, & recirc. This was my first non-defroster linked system and I liked it much better. You had full control over everything no matter what. It had a variable disp. compressor which would stay on continuously as long as the A/C button was depressed.

2007 VW Rabbit:

Wife's old car, Manual fan, A/C, recirc. but automatic temp control. Climatic is the term used. If you look in the middle of the button stack you can see a black dot which was an infrared temp sensor. It would maintain 72F the best it could but you had to adjust fan speed/A/C usage. Another non-linked defroster setup but because the blend doors were electric you could not use recirc. in any defrost mode. It would blink the button light and not come on or turn off if already on. Another variable displacement compressor as well and one [censored] of an A/C system. High fan, w/ recirc. on it could freeze you out of the cabin easily.

So Max A/C only meant something on the Caprice, other cars common sense stepped in which a lot people don't have. Which I feel is why you see it on a 2011 car. People are a little dumb to realize you can't effective cool a car if you are constantly pushing in 98F air.

Max A/C has nothing to do with keeping the compressor on longer in non-variable systems and everything to do with public perception. On variable systems it could force the use of 100% A/C for a short amount(in theory I have no proof) of time but as was already mentioned the car will throttle back to prevent icing of the evaporator. There is no way around that.

 

[ekpolk]

Thermo:

Thank you for reinforcing, very well I might add, the point I was trying to make in an earlier post: we're not all talking about the same thing. It's not as if there's some government-mandated standard meaning for a "Max AC" button/feature. It does different things in different cars, if it's there at all.

 

[Hokiefyd]

Originally Posted By: ekpolk
Yes, when you select the MAX setting, the car automatically goes to the RECIRC mode. BUT you can stay in the MAX mode, AND turn RECIRC off too if you choose that option.


That's not how any system that I've owned operates, and that's not how the 2011 Camry's system operates. If you move the temperature dial down to MAX A/C, the RECIRC light illuminates. Pressing the RECIRC button does nothing at this point. Using MAX A/C locks the HVAC system into RECIRC mode. You can bring the system out of MAX A/C by turning the temperature dial one step up (to full cold), and THEN, you can turn RECIRC on and off as you please. But in MAX A/C, RECIRC is on by definition.

Originally Posted By: ekpolk
RECIRC and MAX really are not the same thing. In an of itself, all RECIRC does is determine whether the car will draw in air from the outside, or whether it will not.


It's obvious that different HVAC systems operate differently. But in my Camry, MAX A/C is the same as using RECIRC and A/C and full cold, all at the same time. MAX A/C is simply a much simpler way to get there (as Thermo said above, an easy way for the public to operate the system)

My minivan doesn't have a "MAX A/C" button. To use "MAX A/C", you turn the dial to full cold, make sure the A/C compressor is engaged with the snowflake button, and press the RECIRC button. It simply doesn't have a MAX A/C shortcut button that some systems do.

 

[Thermo1223]

Originally Posted By: ekpolk
Thermo:

Thank you for reinforcing, very well I might add, the point I was trying to make in an earlier post: we're not all talking about the same thing. It's not as if there's some government-mandated standard meaning for a "Max AC" button/feature. It does different things in different cars, if it's there at all.


No problem, it does seem a personal thing with each car maker.

My Subaru has no setting saying that and even for being auto climate control will let you turn recirc. on & off no matter what option you pick on the dial. The same goes for A/C if memory serves except of course when cold.

 

[Hokiefyd]

Originally Posted By: ekpolk
I'm pretty convinced at this point that the "disagreement" in this thread is not based upon anyone's fundamental lack of understanding, but rather that different cars are designed/programmed to work in different ways.


Yes, I'll certainly agree with that.

 

[SteveSRT8]

very different.

Most GM products, especially larger vehicle, recirc is only 85%. They will not allow 100%, it's always got a little outside air.

I have one car that slams the door shut, recirc gives 100% and gets super COLD. I like it better that way.

 

[ekpolk]

Originally Posted By: Hokiefyd
Originally Posted By: ekpolk
Yes, when you select the MAX setting, the car automatically goes to the RECIRC mode. BUT you can stay in the MAX mode, AND turn RECIRC off too if you choose that option.


That's not how any system that I've owned operates, and that's not how the 2011 Camry's system operates. If you move the temperature dial down to MAX A/C, the RECIRC light illuminates. Pressing the RECIRC button does nothing at this point. Using MAX A/C locks the HVAC system into RECIRC mode. You can bring the system out of MAX A/C by turning the temperature dial one step up (to full cold), and THEN, you can turn RECIRC on and off as you please. But in MAX A/C, RECIRC is on by definition.
I may be recalling it wrong, but in the last manual AC system car I owned, which was a 2003.5 V-6 Camry, you COULD deselect RECIRC which would have activated automatically when you went to MAX. This would leave the system making its maximum effort to cool, but while drawing in fresh air vs recirculating.

Originally Posted By: Hokiefyd
Originally Posted By: ekpolk
RECIRC and MAX really are not the same thing. In an of itself, all RECIRC does is determine whether the car will draw in air from the outside, or whether it will not.


It's obvious that different HVAC systems operate differently. But in my Camry, MAX A/C is the same as using RECIRC and A/C and full cold, all at the same time. MAX A/C is simply a much simpler way to get there (as Thermo said above, an easy way for the public to operate the system)

My minivan doesn't have a "MAX A/C" button. To use "MAX A/C", you turn the dial to full cold, make sure the A/C compressor is engaged with the snowflake button, and press the RECIRC button. It simply doesn't have a MAX A/C shortcut button that some systems do.

I suppose that for many vehicles, seeing the MAX AC button as a form of "shortcut" makes sense. At the moment, all three of our cars (see sig, below) have fully automatic systems, and none of them include a "MAX AC" button. You set the temp you want, make sure the AUTO button is lit, and let the computer worry about it from there. It's very effective, and the only time I need to make further input is occasional changes to the direction of airflow, via the "manual" vanes on the output vents themselves.

While there is no "MAX" setting per se, there is a limited range of temperatures. Being in the office, I forget the particular numbers, but IIRC, it's 65 deg F on the cold side and 85 on the hot, for the Camry (might be off by five on either -- the system works so well for real-world use, I never set the extremes, except occasionally from simple curiosity). If you exceed those numbers, you see LO or HI on the display instead of a number, and the system seems to go into an "open loop" attempt to pump out as much cold or hot air as it can, as fast as it can. You can make the car bitter cold or burning hot very quickly.

I suspect that the LO/HI open loop alternative to the closed loop attempt at achieving a particular temp is the analog (bad pun, sorry) to the old "MAX AC" option (whatever that actually did) on manual climate systems.

 

[dwendt44]

The Owners Manual should say what each fuction operates.
Since it's a new(er) car, the manual should be available to you.

Read it.

 

[ekpolk]

Originally Posted By: dwendt44
The Owners Manual should say what each fuction operates.
Since it's a new(er) car, the manual should be available to you.

Read it.


Yeah, well, if we didn't have severely dumbed-down manuals that effectively tell you nothing more than to do routine maintenance and fasten your seatbelts, well then we might actually learn something from reading them. I've read my O/M from cover to cover and it tells you very little beyond how to set the controls, and not much of that. Don't be venting on customers for not reading their manuals when there's little of true substance in them. Reading the O/M today is like eating a Twinkie and hoping to get some nutrition. There's some there, and some calories, but little else.

 

[bigmike]

Isn't that the truth!

It'll go on for 50 pages on how to buckle a car seat or how to play your stereo, but nothing when it comes to stuff you'd really like to know.

 

[Samilcar]

Originally Posted By: ekpolk
Originally Posted By: Hokiefyd
Originally Posted By: ekpolk
Yes, when you select the MAX setting, the car automatically goes to the RECIRC mode. BUT you can stay in the MAX mode, AND turn RECIRC off too if you choose that option.


That's not how any system that I've owned operates, and that's not how the 2011 Camry's system operates. If you move the temperature dial down to MAX A/C, the RECIRC light illuminates. Pressing the RECIRC button does nothing at this point. Using MAX A/C locks the HVAC system into RECIRC mode. You can bring the system out of MAX A/C by turning the temperature dial one step up (to full cold), and THEN, you can turn RECIRC on and off as you please. But in MAX A/C, RECIRC is on by definition.
I may be recalling it wrong, but in the last manual AC system car I owned, which was a 2003.5 V-6 Camry, you COULD deselect RECIRC which would have activated automatically when you went to MAX. This would leave the system making its maximum effort to cool, but while drawing in fresh air vs recirculating.


This might have been something that Toyota has changed just recently. Our 2008 Sienna with manual AC operates exactly as Hokiefyd describes. If you go one click too low on the temperature knob, RECIRC locks in and can't be turned off unless you turn the temp knob up one click. This "feature" bugs me to no end.

 

[brianl703]

Originally Posted By: ekpolk

Reading the O/M today is like eating a Twinkie and hoping to get some nutrition. There's some there, and some calories, but little else.


You shouldn't have to read the service/shop manual to find out what the MAX AC setting does, but that's what it might take.

 

[Hokiefyd]

Originally Posted By: Samilcar
This "feature" bugs me to no end.


Why does that bug you/how would you prefer it to operate?