Silvex

Is the exhaust gas sensor always active?

Or is it only active in Automatic Air Intake Control and Automatic Climate Control mode?

Also, do all recent Lexus models have this exhaust gas detection feature?

I'm trying to get my head around how the recirculated and outside air functions work in our cars.
In particular, my IS 250 F-Sport MY2011
That has the Type A Air Intake Control system (Recirc/Auto/Outside three-way button), as some of you may know.

There is a wealth of information, tips and advice on CL forums.
I am finding that most useful.

I'm posting this on the IS-F Forum because I believe the cars all have Type A AIC set ups.

Silvex

lobuxracer

iTrader: (2)

The gas sensor only works in the auto position. It can only change from outside air to recirculate. If you are hard set to either of these settings, the gas sensor's input is not used. The HVAC on the IS-F has not changed since 2008. The New Car Features manual has an extensive (23 page) document on how all this works. It is available on TIS.

Silvex

lobuxracer, thanks very much.

That is exactly what I've been wanting to know.
Thanks for explaining it so succinctly.

I was slowly coming round to that explanation by carefully reading the excellent posts on CL.
But there is some well meant opinion and speculation out there.
So it's a great relief to have it confirmed by someone like you.

<The New Car Features manual has an extensive (23 page) document on how all this works. It is available on TIS.>
I really would like to know as much as I can about the Air Intake Control function.
So I'll take out a 2 day subscription to study that 23 page document.
I hope they will accept my English £s equivalent to $15 !

Would you be able to point me exactly to where I can find that document in the TIS "library" ?

Another quick question please.
When the blower is on, but A/C is not on
When you press the IAC button to activate say, AUTO OUTSIDE AIR mode.
Why is A/C always switched on?

Silvex

Silvex

lobuxracer, just reading through your comment again this morning.

Just making sure I've got it.

When you say "The gas sensor only works in the auto position."

Is that the Automatic Air Intake "auto position" (three-way button)?

Or is it the Automatic Climate Control "auto position" (big AUTO" button" ?

Silvex

lobuxracer

iTrader: (2)

Both are required to be in the auto mode. Turning the A/C compressor off disables the auto function (at least on my car), so the auto recirc/fresh setting goes away as well.

Honestly, I think the implementation leaves a lot to be desired. I see no reason to have the A/C cooling the interior when outside air temp is at or below the target temperature, but this is the only way the system works. IMHO, it is the Achilles' heel of this design.

Not sure how the access to TIS works from a European IP address. If it did not flagrantly violate copyright, I would post the doc here.

Silvex

<Both are required to be in the auto mode. >
Boy, am I glad I asked this question.
Thanks very very much.

I've spent more time than I dare to admit to, experimenting with these settings.

I just could not figure out if it was Auto CC, Auto IAC or both, Auto CC and Auto IAC.
Every time I thought I'd solved it, something else turned up to disprove my theory! :-)

I'm pretty sure that there is nothing explicitly in the Owner's Manual about this.
That is, you have to have both Auto CC and Auto IAC on, so gas is detected.

I would need to go out to the car and check.
But I think when you turn A/C CC on, the Auto IAC comes on too.

Either Recirc/Auto or Outside/Auto.

You can then hard set (as you so elegantly put it earlier) to Recirc or Outside setting.

That does not turn A/C off of course.

<Honestly, I think the implementation leaves a lot to be desired.>
I'm very pleased to hear you say that.
I thought it was just me.
When I've asked dealers, they look at me as if I'm crazy. Ha-ha
Well maybe I am, for persevering for so long :-)

<Turning the A/C compressor off disables the auto function ....>
Yes, exactly the same here.

<I see no reason to have the A/C cooling the interior when outside air temp is at or below the target temperature, >

Do you think that in certain conditions, it might be because the system is trying to get rid of excess humidity in the air?

That is,drying the air by passing it past an active evaporator.

That would help stop any window fogging, right?

Silvex

lobuxracer

iTrader: (2)

Yes, the A/C is for humidity control, but it is completely arbitrary and implemented with extreme prejudice. Since there is no humidity sensing input, the system assumes outside air is too humid and will not save a bit of petrol needed to run the heat pump when outside air into the cabin would be completely appropriate. Sure it's another sensor which could fail, but I know I'm not the only person to see this as an annoyance. I have worked around this by shutting off the A/C manually in the spring and fall when OAT is in the very liveable and comfortable range. It does save fuel from my empirical results - I see best fuel economy in these times of year regardless of the type of driving (off the track) I'm doing.

Silvex

lobuxracer, thanks. Very helpful.

<...but it is completely arbitrary and implemented with extreme prejudice.>
Wow! Noted.

<I have worked around this by shutting off the A/C manually in the spring and fall when OAT is in the very liveable and comfortable range.>
Good idea. I'll try this too. If it can save a bit of fuel, all the better.

Earlier you said
<I see no reason to have the A/C cooling the interior when outside air temp is at or below the target temperature, but this is the only way the system works. IMHO, it is the Achilles' heel of this design.>

I've been thinking about this.
I think I can understand what you are saying.

When Auto IAC is selected, A/C is automatically switched on.
You cannot run Auto IAC without A/C being on.
It doesn't matter if OAT is below the target temperature.
You can't turn A/C off and rely on cool OA and, leave Auto IAC on.
If you want to run Auto IAC, you _have_ to have A/C on (even if you don't need it on)

If you turn A/C off, Auto IAC is turned off, automatically.

Have I got this right?

If so, you know what I'd like to ask now?

Why did they design it like this i.e. A/C to come on when Auto IAC is selected?

Silvex

lobuxracer

iTrader: (2)

You have it correctly. No idea why other than the A/C offers humidity control by reducing the humidity. 25C can feel quite different at 10% RH vs. 90% RH. If the system defaults to drying the air with the A/C, it will feel consistent regardless of outside humidity. I suspect this is the reasoning behind their choice.

Silvex

Ok thanks.

<If the system defaults to drying the air with the A/C, it will feel consistent regardless of outside humidity.>
That does make sense.
I can see how the Lexus designers are trying to automatically give us the best possible cabin environment here.

But just to be certain I've understood, can you confirm the following please.

When you say <25C can feel quite different at 10% RH vs. 90% RH.>
Are you referring to OAT/outside humidity?

Silvex

lobuxracer

iTrader: (2)

Not specifically OAT, but definitely ambient humidity. The thing the system does not know is the ambient humidity, so if it defaults to drying the air with the A/C, so they know the humidity in the cabin will be in a very small range which means all their calculations for comfort will work. Without controlling humidity, their calculations could be spot on, or far and away from their expectations, so they default to a low humidity environment provided by chilling the air first, then adjusting the temperature with the heater core and fan. It's the only way for it to work consistently day to day and season to season.

Silvex

Now, this is really interesting and very useful to know.

Earlier you said "Since there is no humidity sensing input, the system assumes outside air is too humid and will not save a bit of petrol needed to run the heat pump when outside air into the cabin would be completely appropriate."

Aha! So are we saying that even when there is really no need at all for the compressor to run, it goes ahead and does it?
Because it always wants to dehumidify the air to deliver a low humidity environment from which the comfort (and safety, I presume?) calculations can be based?

If so, this may be yet another huge shaft of light that has helped clarify my understanding of what is going on!
The idea that when the A/C indicator in the Nav screen is illuminated (yellow), really does mean the compressor is working, right?
It is not (or at least, very rarely) on Stand-by, as others have suggested?

I note also that you said, "I see no reason to have the A/C cooling the interior when outside air temp is at or below the target temperature, but this is the only way the system works. IMHO, it is the Achilles' heel of this design."

I'm sorry that I appear to be making you repeat yourself.
But it is definitely worth it, for me at least. Thanks.

<I have worked around this by shutting off the A/C manually in the spring and fall when OAT is in the very liveable and comfortable range. It does save fuel from my empirical results - I see best fuel economy in these times of year .... >
I have being experimenting with this myself.
The results are very positively surprising.
With just me in the car, the cabin environment is just fine.
That is, with A/C off.
Ambient temp at the moment is 8 -10C
And also, with Auto CC off too.
I had not realised how finely tuned those rotary air distribution vents (flow rate and direction) are.
They seemed to have been made by a watchmaker!
I can get the flow and direction exactly, how I like it.
But, with my wife in the car, she complains about the air quality.
She can tell I've got the A/C off :-(
Another passenger is +100%, = more humidity I guess.. If you see what I mean ...

Silvex

Defratos

lol just trying to follow this thread right now is giving me a headache....I'll try and understand it tomorrow morning G'night

lobuxracer

iTrader: (2)

They mitigate the losses with a variable compressor for the A/C. It's actually pretty impressive because it's very efficient, but in the end, if you shut it off IME, you save fuel.Never ask a woman about air temperature. Their sense is completely different from the male sense, and all you will do is confuse yourself. Set it to what ever makes her happy. Happy wife, happy life. IOW, do what she asks, then shut up and color if you want to keep your life simple.

Silvex

Ha-ha, I think you'll find it's well worth trying to understand.
Then you can help me! :-)

<The variable displacement compressor has a swash plate that rotates to reciprocate pistons, ... >
Unless you're a guru like lobuxracer, don't read this part of the discussion before you go to bed at night. You'll never get to sleep, if you're like me :-)

Seriously, I look forward to any input you can give us.

Silvex