Please Explain The Defroster

[intensifi]

Sorry for the dumb question but what is the best way to defrost the front window?

I can turn the defroster on, but turning it off and leaving it in a quite enough mode to keep defrosting is not clear to me.

The manual says something about adjusting the fan speed, vent flow, ac mode after pressing the defrost button, etc.

Please help!

[skyfish400h]

Sorry for the dumb question but what is the best way to defrost the front window?

I can turn the defroster on, but turning it off and leaving it in a quite enough mode to keep defrosting is not clear to me.

You can use the defrost windscreen button on the dash if you are in a panic situation and need to clear without doing alot of fiddling with controls. But in my opinon that is ALL that button is good for. BTW, the defrost mirrors and rear window work just fine and should be turned on.

If you really want to defost the windscreen then you need take manual contol by going into the CLIMATE contol on the NAV screen.

Key settings are as follows:

Flow contol set to aim at the windscreen (and maybe your feet too, if they're cold).

Fan speed should be adjusted as needed to maintain vision ( on HIGH at first ).

Circulation should be set to RECIRCULATE (this is important for the next bullet to be effective)

Most importantly: Turn on the AC to dehumidify the air inside the car. You can turn this off once the air inside gets dry enough. If you stop and get out or if you are wearing wet clothes/boots... you will likely need to just leave it on.

Adust temperature to comfortable level given the number layers you are wearing ;)

[wwest]

skyfish400h, your directions are quite good for "so cal" but can be dangerous, even deadly, in moderately cool and humid or wet and COLD climates.

First, probably a totally useless point of clarification, but the A/C cannot be effective, whatsoever, in defrosting the windshield. Defrost implies frost, and that is a circumstance that is virtually EXCLUSIVE to the exterior surface of the windshield.

But, like you, I suspect the post has to do with interior windshield defog/demist rather than actual defrost, as that is one of the major flaws in the design of the Toyota/Lexus automatic climate control.

Becuase of the inherent flaws in these systems designed by NipponDenso, Denso US, it is highly advisable to always keep the A/C system off, or completely disabled, when the OAT is predominantly cool, say below 55F.

Yes, the A/C can sometimes aid in the effort/need to defog/demist the windshield, but from the owners viewpoint that capability is completely and totally unpredictable. The efficiency of the A/C to dehumidify the incoming FRESH airflow is totally dependent on outside climatic conditions.

Because of the unique design of the Denso climate control airlfow routing, for which they actually hold a US patent, it is a practical impossibility to have the climate control operating at a reasonable human comfort temperature level and keep the interior windshield surface clear of condensation at the same time.

The best answer I can give you is to leave the system in defrost/defog/demist mode with the temperature setpoint set as far above your personal comfort level as you can stand and then use the blower speed manually to control overall passenger cabin comfort.

As of 2001 Lexus introduced two new c-best options, one to allow you to disable the A/C indefinitely and the second to unlink the A/C from automatic operation (with no indication of same) in defrost/defog/demist mode.

I also noticed that as of 2005 the system will automatically switch from cooling mode to combined heating and defog mode if the OAT declines to or nearly freezing. That will very likely result in not just a few accidents, injuries and maybe deaths, before Toyota realizes that "switch" should be done at ~45F if the trend is outside temperatures are lowering.

Once the passenger cabin's atmosphere is acclimated to your temperature setpoint it will automatically default into cooling mode. Not only will this be significantly discomforting to you on a night, or day, when the surrounding landscape is predominantly cool or cold, it doesn't allow any warming airflow to the interior surface of the windshield.

So as you drive along feeling somewhat chilled due to radiant "cooling" from the surrounding landscape and cool and dry airflow directed to your face and upper body, the windshield is being thoroughly CHILLED due to the cold airflow impinging on the exterior surface at roadspeed.

Eventually the interior surface of the windshield will be lowered to the dewpoint of the cabin atmosphere and you will have a real problem on your hands.

Keep in mind that once the A/C has been used, even as much as 24 hours ago, a significant level, thin film, of moisture will always remain on those roughly 10,000 square inches of evaporator cooling vane surface area.

That's why and how that horrid mold and mildew, dirty gym socks, odor developes within the A/C plenum. Those microbes just dearly love breeding in that damp, dank and dark environment.

See the EED, electronic eveporator dryer description at airsept.com for more information.

[Rx330driver]

While were on the subject of defrosting, theres something i want to clear up (no pun intended). When i click the button for the defroster for the front winshield, the air obviously turns on and it sounds like its on medium high. I click my nav screen to climate and i the LOW button is highlighted. So then i click on the low button again and it finally goes to the low setting. Anyone getting this?

Edited December 27, 2005 by Rx330driver

[wwest]

Until the cabin atmosphere has warmed to your temperature setpoint, or closely nearby, the actions in defrost mode will differ. If you activate the defrost/defog/demist mode during cabin warm-up then the assumption is made that your intend is to remove frost from the exterior surface. Therefore in this mode at this "time" you will get a reasonably high level of heated airflow to the interior windshield surface.

After the cabin has acclimated to you setpoint all you will get in defrost/defog/demist mode is a low level of "tepid" airflow, perhaps even 20F cooler than that required for footwell heating mode airflow.

You may note that in this mode the system's "auto" light is not longer on. That's because the defrost/defog/demist mode is considered a "special" function whereby the airflow level (blower speed), warmth, airflow direction, and A/C operation are not in line with your "automatic" settings.

You may also note that if you have previous turned the A/C off it will still automatically operate, without an indication of same, in this mode. That's provided you haven't had the dealer set the C-best options.

If you wish to "leave" defrost/defog/demist mode and return to your previous automatic mode settings simply depress the defrost mode switch momentarily as it states in your owners manual.

[skyfish400h]

skyfish400h, your directions are quite good for "so cal" but can be dangerous, even deadly, in moderately cool and humid or wet and COLD climates.

While I will not take any offense at your casual dismissal of my post due to my stated location, I must take issue with your characterization of my post as "dangerous" or "deadly". While I do not enjoy guru status on this board, I do have some experience with driving in snow and cold conditions in a variety of vehicles.

It is from my experience that I have determined that the best way to control the winshield visiblity is to take manual contol in any vehicle. Also, using the A/C as a dehumidifier works very well indeed for defogging and has no detrimental effect on deicing when used along with the RECIRCULATE option.

But, like you, I suspect the post has to do with interior windshield defog/demist rather than actual defrost, as that is one of the major flaws in the design of the Toyota/Lexus automatic climate control.

Becuase of the inherent flaws in these systems designed by NipponDenso, Denso US, it is highly advisable to always keep the A/C system off, or completely disabled, when the OAT is predominantly cool, say below 55F.

Yes, the A/C can sometimes aid in the effort/need to defog/demist the windshield, but from the owners viewpoint that capability is completely and totally unpredictable. The efficiency of the A/C to dehumidify the incoming FRESH airflow is totally dependent on outside climatic conditions.

We are in agreement then that the AUTO and DEFROST buttons on the dash are next to useless. When you use these you are at the mercy of the algorythum designer and s/he is not riding in the car with you.

You correctly point out the difficulty in managing the humidity of the FRESH air as it will change given the contitions outside. That is why I made a point to say that you should use RECIRCULATE to avoid this issue.

Because of the unique design of the Denso climate control airlfow routing, for which they actually hold a US patent, it is a practical impossibility to have the climate control operating at a reasonable human comfort temperature level and keep the interior windshield surface clear of condensation at the same time.

The best answer I can give you is to leave the system in defrost/defog/demist mode with the temperature setpoint set as far above your personal comfort level as you can stand and then use the blower speed manually to control overall passenger cabin comfort.

As of 2001 Lexus introduced two new c-best options, one to allow you to disable the A/C indefinitely and the second to unlink the A/C from automatic operation (with no indication of same) in defrost/defog/demist mode.

I also noticed that as of 2005 the system will automatically switch from cooling mode to combined heating and defog mode if the OAT declines to or nearly freezing. That will very likely result in not just a few accidents, injuries and maybe deaths, before Toyota realizes that "switch" should be done at ~45F if the trend is outside temperatures are lowering.

Once the passenger cabin's atmosphere is acclimated to your temperature setpoint it will automatically default into cooling mode. Not only will this be significantly discomforting to you on a night, or day, when the surrounding landscape is predominantly cool or cold, it doesn't allow any warming airflow to the interior surface of the windshield.

So as you drive along feeling somewhat chilled due to radiant "cooling" from the surrounding landscape and cool and dry airflow directed to your face and upper body, the windshield is being thoroughly CHILLED due to the cold airflow impinging on the exterior surface at roadspeed.

Eventually the interior surface of the windshield will be lowered to the dewpoint of the cabin atmosphere and you will have a real problem on your hands.

Thank you again for making my point about how it is a BAD IDEA to trust the automatic controls in a situation where your safety is at stake. Take MANUAL contol of EVERY aspect of the sysytem... Speed/temp/flow/source/humidity... understand how each one affects your visiblity... and you will do fine. I fully endorse having the dealer set your c-best options to give you manual control of the A/C operation and to disable the AUTO default at powerup.

As for your "best answer" above, I find it lacking. You offer no clear direction in your post and seem to prefer to watch yourself type.

something about ...dirty gym socks... deleted.

[wwest]

Deleted.

[wwest]

Yes, the A/C will be more efficient in dehumidifying the airflow if recirculate it used. But a serious trade-off is involved here. If you use recirculate continuously then there will be little or no cabin atmosphere "flow-through".

With human metalbolism being as it is the cabin atmosphere will slowly become more stale and humid.

In order to improve MPG when using the A/C year 'round, modern day vehicles, even non-luxury ones, are extremely well insulated and sealed. Even the "opening" of the cabin atmosphere outflow "exhauster" has been downsized to retrict the outflow of previously "conditioned" air and thereby reduce the need for the more A/C compressor cycling.

But the real danger is having the A/C compressor shut down if or when the outside air temperature declines to or nearly to the freezing level. Once the A/C shuts down, and it will (generally with no noticeable indication, no aleart or alarm, to you) the cabin atmosphere, at your ~70 comfort level, will quickly result in the evaporation of the previously condensed moisture still on the evaporator vanes, into the cabin airflow.

Talk about sudden and complete windshield fogging...!!

So yes, the act of using the A/C to aid in defogging the windshield or keeping it defogged will oftentimes be helpfull and certainly not harmful in and of itself.

But look what happens if and/or when you turn it off with all that previously condensed mositure still on the evaporator vanes. It will often quickly evaporate into the airstream and thereby into the cabin.

Cars with air conditioning have always endured episodes of mould and mildew odors and windshield or window fogging, but in about 1990 the industry started changing automotive designs in ways that inadvertently led to a dramatic increase in these instances.

Better insulating, sealing and sound deadening materials all result in more "containment" of the cabin atmosphere. Intentional downsizing of the cabin atmosphere's exhauster port so "conditioned" air could be held, maintained, within the cabin longer.

At the same time due to growing space limitations (no pun intended) within the front dash area the A/C evaporator was downsized again and again. So nowadays we have 10,000 square inches of evaporator cooling vane surface area collapsed into a very small space, think "sponge".

Operate the A/C, give these modern day A/C evaporators 24 hours to "dry" out in a warm garage with the windows closed, and you still have about a pint of liquid left, as a thin film of condensate, on those vanes. Another quart or so will have evaporated off the vanes in that 24 hours but is in all likelihood still within the A/C plenum area in airborne vapor form. The atmosphere within the plenum is very likely super-saturated with moisture.

So you start down the road the next "cool" morning, the system blower doesn't start up until the engine water jacket has reached 130F, 2 to 5 miles down the road, and POOF, your windshield is suddenly fogged over to the point where you have absolutely no forward view.

The windshield fogging problem is further exacerbated by the uniqueness of automatic climate control designs by NipponDenso, Denso US, used exclusively by Toyota and Lexus and many other vehicles of asian origin. Denso UDS actually holds a US patent on this unique design, cooler system airflow predominantly to upper cabin areas and warmer system airflow restricted to footwell and lower cabin airflow areas.

Regretably while inherently a good concept its implementation in most cases inadvertently results in the inability to quickly defog or demist a window or windshield. In order to get warm and dry airflow to the interior surface of a fogged over windshield the internal system airflow must be reversed, baffled, at the footwell plenum outflow exit, if order to force the "reheat" flow to the windshield ducts.

So Airsept's EED device will have a substantial market for the foreseeable future and not jsut a few accident will result from episodes of inadvertent and sudden windshiedl fogging in cool or cold weatehr conditions.

In the meantime either find a way to disable, completely, the A/C compressor during the winter months, or park your car in a warm garage each and every night with the windows open slightly to allow the previous day's condensate to evaporate and allow convection airflow to remove most of the resulting airborne moisture.

Edited December 30, 2005 by wwest

[MrLANlord]

Hello all. I'll be receiving my 400h on the 18th of the month. Yay! I just found this forum (had been reading clublexus.com). I can't believe my first post will start so completely off the posted topic. For that, I apologize sincerely.

With that said...I have read a total of maybe 8 threads so far. In 2 of those first 8 (25%), 'wwest' has predicted bodily harm and/or death for drivers of the RX400h. How in the world did such a life-threatening vehicle ever make it onto the road? LOL

Back on topic....Manual control of the system tends to produce better results in my experience with other Lexus and Toyota vehicles. However, that is just my opinion as I hold no degrees in climatology. Your mileage and life expectancy may vary.

Edited January 11, 2006 by MrLANlord

[wwest]

The only reason FWD vehicles ever made it to public use is because they are so inexpensive to manufacture as opposed to RWD.

Luckily the trend is currently and clearly going the other way.

The AWD versions of the Lexus IS and GS will automatically apportion engine torque primarily to the rear if the VSC system detects, senses, via the yaw sensor, that the front tires' contact patch should be dedicated to maintaining lateral, directional control.

The Volvo XC90 uses an AWD system that dynamically allocates engine torque. With the XC90 as you enter a turn/curve the engine torque is primarily routed to the rear and as you reach the apex of the curve it begins re-apportioning engine torque to the front.

99.99% of the time, for many of us, none of that matters. But since there is no way for the manufacturers to detect an approaching slippery surface it's that 0.01% that they are protecting you from.

With the RX400h the front tires recieve 100% of the driving torque regardless, right up until you encounter that 0.01% roadbed condition. So in YOUR case as you approach the apex of that turn and the lateral stress on the front tires' is climbing rapidly the engine drive forces are additive to the lateral forces.

And, yes, the instant one or both front tires' loose traction with the roadbed the rear motor will start producing drive torque.

A REACTIVE system or a PRO-ACTIVE, AWD system, which would you rather drive?

Do you ever wonder why the manufactuers didn't go to rear engine rear wheel drive back in the late 70's instead of FWD....?

I certainly do.

Maybe it was Nader's fault.