Rx400H A/c "re-Circulate" Button Annoyance; Smog Sensor?

[jaswood]

That's the thing though, i don't care about the "A/C" being activated- the only problem i am having is with the "inside" vs "outside" air settings changing on their own without me hitting ANY buttons. As far as the "A/C" feature goes, if i press it ON it stays ON until i press it OFF. I'm not sure what it does when i turn on the defrosters, but whatever it's doing to the "A/C" is fine with me. The only thing i do notice when i turn on defrosters, is that it turns "outside air" ON until i turn the defrosters OFF- this i like however!' My issue is only with the fact that it toggles between "inside" and "outside" air at random times without me touching any buttons. I don't have the system set to "AUTO", i don't have the defrosters on; yet it still changes on its own...

There are a few things that will result in the A/C cooling/dehumidification system being shut down automatically.

If you are in "recirc" mode when that happens I have little doubt that the system will then automatically switch to "fresh".

1.) If you drive into an area of sub-34F temperature.

Note: Driving OUT of a decently warm garage into COLD weather the A/C system switch off a few miles down the road.

2.) If the engine coolant begins to rise toward the point of overheating.

NOTE..not actual overheating, just close-by.

There might be other causes, those are the ones I have encountered or know about.

[cduluk]

Why do you keep mentioning A/C? I don't have a problem with the A/C switching between ON and OFF.

[jaswood]

My RX was in today for the pulley recall (turns out I needed a replacement). I had an ES350 (I think that's what it's called..lol) for a loaner. Sure enough, it wouldn't stay in recirc for any decent amount of time (I was driving so I didn't time it). One thing it did have for the recirc button was ON, OFF and AUTO. I have no idea why they have AUTO when the damn thing does whatever it wants anyway...lol.

I have no idea why my RX stays in RECIRC (except mine is a 2006 and Cduluk is a 2008 - software program changes??)

On another note, isn't kind of sad that the majority of the motoring public are too clueless to know to switch

"...from fresh to recirc if the windows start fogging up..."

Why else would car manufacturers need to program the recirc to switch off automatically...

Was that a typo or was backwards intentionally...?

Don't ALL modern day systems switch AUTOMATICALLY to FRESH when you activate defrost/defog/demist, or even partial windshield flow...?

Ack...lol. Backwards. I mean too clueless to switch from RECIRC to FRESH if the windows start to fog up. Yes, that's my point. The car does it automatically now because most people don't think to do it themselves. Every winter I see older Toyota Corollas and Honda Civics with all the windows fogged up and I can almost guarantee that they are driving around with RECIRC on.

"...every winter I see older...don't think to do it themselves.."

Maybe, maybe NOT.

Asian manufacturers use NipponDenso climate control designs pretty much exclusively. Going back to the late eighties and well into the ninties, mayb even today, these design were quite seriously flawed insofar as defogging windshield/windows and keeping them defogged.

NipponDenso designs of that era relied EXCLUSIVELY on the dehumidification capability of the A/C for the task of keeping the cabin atmosphere below the dewpoint of the interior windshield surface.

Given that mother nature has full control of the effectiveness of that task it rarely works in certain climatic conditions.

To make those systems workable insofar as defogging the windshield and keeping it that way the driver HAD TO KNOW to crank up the HEAT simultaneously with switching to defrost/defog/demist mode.

The thing that made that quite confusing was/is that until the cabin temperature was raised to with a few degrees of your temperature setpoint the system would use HEAT and, along with, the A/C.

But then there was yet another NipponDenso design flaw that was/is important if you happen to own a vehicle with a fully automatic climate control system.

With those systems you had to know about an unpublished aspect of the operation of the system. In fully automatic mode the system, without ANY indication to you, would modulate, linearly modulate, between "fresh" and "recirc" in accordance with certain control parameters.

You had to know to follow up with putting the system in "auto" mode and then depress the "fresh" PB in order to lock the system in "fresh" mode. Otehrwise even with the "fresh" PB indicator illuminated the system might be 80% in recirc mode.

On a cold winter day, DANGEROUS, that.

[jaswood]

Why do you keep mentioning A/C? I don't have a problem with the A/C switching between ON and OFF.

Because, as a matter of safety, the operational mode of the A/C bears directly on the ability for the system to remain in recirc mode, or in some cases even switch into recirc mode.

And be aware that should the system automatically switch the A/C off for one of the aforementioned reasons although it appears that you can over-ride the A/C and switch it back on the indicator will illuminate but the A/C compressor will remain disabled until the causative factor abates.

[cduluk]

Why do you keep mentioning A/C? I don't have a problem with the A/C switching between ON and OFF.

Because, as a matter of safety, the operational mode of the A/C bears directly on the ability for the system to remain in recirc mode, or in some cases even switch into recirc mode.

And be aware that should the system automatically switch the A/C off for one of the aforementioned reasons although it appears that you can over-ride the A/C and switch it back on the indicator will illuminate but the A/C compressor will remain disabled until the causative factor abates.

The last time i hit the "A/C" button besides this week during "testing" was probably last October... I've never had to touch that switch unless switching between Summer and Winter months; so if it toggles ON and OFF it hasn't bothered me. The only thing that bothers me is the "inside" vs "outside" air thing. If i tell the car to recirculate inside air, the car should do whatever it has to, to make it work. If that means switching ON/OFF the A/C system, then that's what the car should do. It's the middle of the winter; i don't need any cold air! And i don't remember this issue occurring during summer months...

[jaswood]

Why do you keep mentioning A/C? I don't have a problem with the A/C switching between ON and OFF.

Because, as a matter of safety, the operational mode of the A/C bears directly on the ability for the system to remain in recirc mode, or in some cases even switch into recirc mode.

And be aware that should the system automatically switch the A/C off for one of the aforementioned reasons although it appears that you can over-ride the A/C and switch it back on the indicator will illuminate but the A/C compressor will remain disabled until the causative factor abates.

The last time i hit the "A/C" button besides this week during "testing" was probably last October... I've never had to touch that switch unless switching between Summer and Winter months; so if it toggles ON and OFF it hasn't bothered me. The only thing that bothers me is the "inside" vs "outside" air thing. If i tell the car to recirculate inside air, the car should do whatever it has to, to make it work. If that means switching ON/OFF the A/C system, then that's what the car should do. It's the middle of the winter; i don't need any cold air! And i don't remember this issue occurring during summer months...

"...summer months..."

Unless you interfer with its operation the A/C cooling/dehumidification system will be enabled 24/7.

It is only during the wintertime that the system is likely to shut down due to the OAT being below ~34F.

The A/C system CANNOT be made functional with the OAT below freezing so the only alternative is to disable the recirculate function and thereby prevent the buildup of moisture, rising Rh, within the cabin.

[cduluk]

Before the winter, I turn the "A/C" button OFF, and in the spring I press it back ON. I haven't seen the "A/C" button light activated in months (except for a few minutes the other day when I was doing some testing).

On my 400h, the inside/outside air system is completely independent of the "A/C" being ON or OFF.

[jaswood]

Before the winter, I turn the "A/C" button OFF, and in the spring I press it back ON. I haven't seen the "A/C" button light activated in months (except for a few minutes the other day when I was doing some testing).

On my 400h, the inside/outside air system is completely independent of the "A/C" being ON or OFF.

Top/right column "bullet" page 271 of the 2006 RX400h owners manual.

** The "Floor/Windshield" air flow mode may be applied

automatically, if the outside temperature is below 0C (32F).

(more...)

In my opinion it would be patently foolish to leave the system in recirc when the system goes automatically into windshield defog/demist mode as above.

Page 274 right column, 2nd paragraph...

For example, when the ambient temperature is low, the air

intake mode may change automatically to the OUTSIDE AIR

mode. This is not a malfunction.

Vehicles of asian origin use NipponDenso climate control designs almost exclusively. Due to a design flaw originating back in the late eighties vehicles with these systems have proven to be uniquely subject to instances of sudden, spontaneous, windshield fogging.

Even with the safety measures taken as above to prevent the onset of windshield fogging the problem seemingly persists.

[lemon]

[For example, when the ambient temperature is low, the air

intake mode may change automatically to the OUTSIDE AIR

mode. This is not a malfunction.

And that probably explains why mine stayed in RECIRC when I tested it - it was 5 celsius out. Judging by the weather, I don't think I'll be able to test this in below 0 celsius weather till next winter....

[cduluk]

Why do you mention "windshield/defog" mode? I don't have a problem with this... when i hit the defrosters it goes to outside air- that's what i want to happen.

The vent position (head, feet, head+feet, feet+windshield) never changes on it's own. I leave it on head+feet all the time...

The fact that my system switches from inside/outside air on it's own has nothing to do with defogging "mode". Maybe it does this to reduce the moisture in the vehicle, but i don't care what the car thinks; when i tell it to recirculate inside air, i want it to do it! If at any point i get fog on the windshield i'll hit the "defrost" button and turn it off after a minute...

[lemon]

I think it's obvious....your car hates you.

[cduluk]

I think it's obvious....your car hates you.

You've got that right! ^_^

[jaswood]

Why do you mention "windshield/defog" mode? I don't have a problem with this... when i hit the defrosters it goes to outside air- that's what i want to happen.

The vent position (head, feet, head+feet, feet+windshield) never changes on it's own. I leave it on head+feet all the time...

The fact that my system switches from inside/outside air on it's own has nothing to do with defogging "mode". Maybe it does this to reduce the moisture in the vehicle, but i don't care what the car thinks; when i tell it to recirculate inside air, i want it to do it!

If at any point i get fog on the windshield i'll hit the "defrost" button

The problem is that if you arrive in climatic conditions wherein windshield interior surface fogging becomes a HIGH probability the Lexus/NipponDenso climate control design will AUTOMATICALLY switch into a mode that is most likely to PREVENT the onset of SUDDEN windshield fogging. It does that by AUTOMAICALLY switching the airflow mode to windshield/floor and the system inlet airflow to FRESH. The switch in airflow mode helps via supplying "WARM" system airflow (where there was NONE previously) to help keep the windsheild interior surface somewhat heated, hopefully above DEWPOINT. The switch to outside air is done so as to be sure the RH within the cabin does not increase due to human metabolism, perspiration, breathing, etc.

and turn it off after a minute...

Not good advice.

A bit of a history lesson...

Shortly after purchasing, Oct. '91, a brand new 1992 LS400, I discovered that it had a GREAT propensity for SUDDENLY fogging over the interior windshield surface. My immediate reaction, at first, was depressing the PB for defrost/defog/demist mode. More often than otherwise, AMAZINGLY enough, this often made matters worse, MUCH worse. Upon the activation of the defrost/defog/demist mode I often, within milliseconds, found myself with no forward vision as a result of the density of the windshield condensation.

This turned out to be the result of a MAJOR design flaw within the NipponDenso, Denso US, automatic climate control design that still exists to this very day. What is happening with your RX400h, automatic mode switch to PREVENT (hopefully) windshield fogging, is a back door approach to solving the actual design flaw.

The BEST procedure when one first sees even the slightest bit of interior windshield fogging is to first, IMMEDIATELY, turn the HEAT to MAXIMUM, quickly switch to defrost/defog/demist mode. If the system, as it certain should, does not of itself automatically switch into FRESH airflow inlet mode and HIGHEST blower speed then quickly do so yourself.

The results will be twofold.

1.) The extraordinary HEATING of the system airflow will result in quickly, "MOST" quickly, dispersing the condensation via evaporation. That's because the extraordinarily HEATED system airflow will result in the airflow to the windshield having a very low Rh, relative humidity, and will literally act as a SPONGE.

2.) The interior surface of the windshield will be HEATED by the HOT airflow thereby raising the surface temperature well above the previous dewpoint.

Now...CAUSATIVE factor(s).

Your windshield interior surface began to fog over in the first place due to ONLY one factor. The windshield interior surface temperature declined enough that the dewpoint of the cabin atmosphere was reached.

Now you will need to remain mindfull of the need to keep that windshield surface WARMED well above dewpoint, or in the alternative lower the Rh of the cabin atmosphere. The latter can be accomplished by raising the temperature setpoint slightly, and/or continually PURGE the cabin atmosphere via the use of FRESH mode, and possibly even lowering the rear windows very slightly.