Hey Guys:
I have a 1993 so I do not know if this question is pertinent to those of you with newer SC's, anyhoo, here goes....

When I push the Large Round Temp Control button on the left of the Climate Control, in the facia moulding of the console (above the on-off vol of the radio) I notice the following... Do You?

Even in the winter, if it is 20 degrees outside and I have the dial set for 70 degrees in the cabin, the light on the air conditioner comes on? I then turn it off manually, and when I do the AUTO word indicatior in the LCD panel goes away. However, even so, the unit does act as if it is in AUTO mode, changing the fan speed histogram and speed and mode automatically for the duration of the ride.

Recently, when at speed, when I turned the air conditioner off as mentioned above I am SURE I felt the RPMs change in the engine as if the air conditioner compressor clutch was being released.

So, the question for you all is....

Does yours act the same way? Does the air conditioner light come on when you put your climate control on when the outside air is cold and the dial is set to say 70 degrees for inside temp?

Or perhaps, is there some slight neuance that I am not aware of?

All ears..

 

It does that to dehumidify the cabin....helps cut waaaay back on condensate on the inside of the glass. I always run the compressor on ALL my cars in the winter.

 

Now...read this thread
https://www.clublexus.com/forums/sho...threadid=37883

and see how yours behaves.

 

Ok, I will give that a try and report back to you when I see what mine does. So then the air conditioner in ON with AUTO is normal behavior. Thanks.

 

Your Lexus climate control system has several known design flaws.

Someone at Nippondenso, Lexus' A/C system supplier, decided that if the A/C can be used to dehumidify airflow above 50F OAT, then it would take little improvement to get it to work all the way down to its lowest possible operational threashold, 32F, freezing OAT.

As the air gets colder it cannot "hold" as much moisture, so the A/C system works by chilling the airflow to its dewpoint, the "point" wherein the moisture molecules will spontaneously condense from the airflow onto the evaporator (cooling heat exchanger).

Since the absolute lower limit for doing this, using the A/C to dehumidify, is 32F, as the natural airflow temperature, OAT, declines from about 50F toward 32F it becomes incresingly more difficult to accomplish any substantial level of dehumidification.

But Lexus does give it a good healthy(???) try. The 92 LS400 A/C evaporator has over 10,000 sq inches of cooling vane surface and you will note that the system strives mightly to keep the blower speeds at a very low level. In order to do this the vehicle must be well insulated and the exhaust, exit, airflow path must be severely restrictive. The slower the air moves through the evaporator the more it will be chilled.

The bottom line is for all of their efforts it does not work in certain climates and in certain well defineable circumstances.

Here's what you will notice.

1. The windshield will tend to fog over about 5 miles into your early morning drive, creating a potentially hazardous circumstance.

2. You will ofter smell a rather foul musty odor when the system first starts up, especially so in the spring.

As you have already noted the A/C continues to operate all the way done to about 32F outside air temperatures, OAT. Most of the mositure condensed onto the evaporator vanes will drain out of the system through the provided drain tube.

It has ALWAYS been the case that some of the moisture would remain, especially in the wintertime when temperatures are lower and lexx natural evaporation will occur. Becuase Lexus as seen fit to increase the density and complexity of the evaporator so very dramatically there will be a much greater amount of moisture, about a quart by my measure, left on the evaporator surfaces the morning after, 24 hours measured, you park the car in your garage on a cool winter day.

Most of that mositure will remain within the evaporator plenum overnight awaiting the opportunity to become a moisture "TIME BOMB in your early morning drive.

You can combat this by opening the sunroof and windows slightly in your garage every night so much of the moisture can evaporate away into the great beyond.

Of course as the weather warms into springtime and the overnight temperatures increase, the rate at which mold and mildew grow and thrive in the DAMP and DANK A/C evaporator plenum will also increase dramatically.

Lots of questions about health issues have already arisen over this.

Some manufacturers are now retrofitting their products so that the A/C system blower runs at intermittent intervals to exhaust this leftover moisture, hopefully all the way out of the vehicle (I say hopefully) after the vehicle has been shut down for an hour or so.

But the really BIG problem with these vehicles still remains.

3. You will find it really difficult to use the system to remove condensation from the windshield and windows once the cabin has acclimated to your desired temperature setpoint.

4. Your windshield will sometimes spontaneously, and almost instantaneously in some cases, fog over, and everything you do instinctively will make matters worse.

 

Already read the Sunday funnies, so.....

You will soon note, if you haven't already, that in colder weather once the Lexus climate control system has raised the cabin temperature to within a few degrees of your desired setpoint, it will automatically switch to cooling mode, routing cooled and dry airflow to your face and upper body. it will do this in the dead of winter, even at night, when the OAT is sub-freezing and the radiant cooling effects to your body are ABSOLUTELY CHILLING.

This mode can be VERY DISCOMFORTING.

Nippondenso engineers are apparently unaware of the fact that a great deal of the human body comfort equation, as much as half, is due to radiant heating/cooling effects, not simply local air temperature.

Up until the system reaches this "point", if you activate the partial or full defrost/defog/demist function, the system will automatically raise the blower speed to increase the HEAT flow to the windshield to remove and prevent further condensation.

But once the cabin has acclimated to, or very near, your temperature setpoint, the Lexus climate control system will (attempt to) only use the A/C's dehumidification capability, EXCLUSIVELY, to remove and/or prevent windshield condensation.

Even though that capability is well known to be completely NON-EXISTANT with the OAT below near or below freezing.

As a matter of fact the A/C compressor clutch circuit is designed to open when the OAT declines below 35F !!!

my best example:

We left our home near Seattle on a bright but cold winter day, four of us in the car, a new 92 LS400, headed over the pass to Yakima. AS we approached the pass the weather became colder and colder until on the final incline it was snowing heavily.

It was at that point that I noticed slight wisps of condensation forming on the lower corners of the windshield and I instinctively activated the full defog function.

ZAP...

My entire windshield fogged over almost instantly.

So I turned up the blower speed...

Double ZAP !!

Things got a LOT worse.

I started "toggling" the setpoint temperature upwards but my wife quickly took over that task. So, here I was, in the middle lane with the roadbed slippery with ice and snow and traffic all around me and no forward visibilily.

Then I thought to lower the rear windows and only then did the windshield begin to clear.

So what happened?

The OAT when we left seattle was likely in the forties and so the A/C compressor operated until we reached a point wherein the OAT had declined to a level where it was automatically shut down, likely about 35F. The only possible notice to me of this event, had I even known to watch, would have been the A/C indicator "silently" extinguishing.

I had only owned the car for about three months at this point so I can't really say that I had paid any attention to whether or not the system had already switched to cooling mode. Lexus wanted to blame the problem on the likihood that I had inadvertantly switched the system to recirculate, but I find that very unlikely, especially in light of later occurances of the same effect.

In any case if you look this up in the owners manual you will find that in fully automatic mode in this circumstance there is VERY LITTLE airflow to the interior surface of the windshield. With extremely cold airflow impinging on its exterior surface at 60 MPH roadspeed it likely became COLD.

Then the A/C compressor was automatically shutdown.

Now as the evaporator vane surface temperature began to rise ALL of the moisture just previosuly condensed onto those vane surfaces was now free to evaporate into the cold incoming airstream.

With four of us in the car contributing to the loading of the atmosphere with humidity from our breathing and natural body functions that atmosphere may have already been close to saturation, and now with increasing humidity due to the addition of the humdification of the incoming airstream is it any wonder that condensation began to form on the much COLDER interiro windshield surface?

And then I activated the defog function which routed ALL of that heavily moisture laden airflow toward the COLD interior surface of the windshield. AND THEN when that didn't work I turned up the blower and increased the rate at which the windshield was fogging over.

After a few repeat episodes of this type I learned to be very religious about turning the A/C OFF each and every time I started the car during the colder months.

But I hadn't yet learned the complete lesson.

Early one cold morning I inadvertantly used the defog function as we began a trip down I5 to Portland. The defog function will automatically activate the A/C, of course, jus as most systems do. But it worked to clear the windshield and shortly thereafter I returned the system to normal mode, not noticing nor paying any attention to the fact that the A/C incicator extinguished as I did so.

About ten more miles down the road, just as I entered I5 at the junction of S167, the windshield started to fog over once again and I again (unthinkingly) activated the defog function.

ZAP !! again!

Same routine, instinctively increase the blower, things start getting worse, start toggling the temperature upward, my wife takes over that task. I am in the lft lane using my view of the nearby jersey barrier to maintain my lane position at 65MPH!

Lower the rear windows, windshield begins to clear.

What happened this time?

I "primed the pump", accumulated, condensed a substantial level of moisture on the evaporator vanes the first time I unwittingly used the defog function and that in turn actiavted the A/C compressor.

Once I inadvertantly turn the A/C compressor off it apparently took about ten miles for that accumulated moisture to evaporate into the cabin atmosphere to the point where the cold interior surface of the windshield caused it to decline to its dewpoint.

So...

1. When my 92 LS400 gets parked in the garage at night I open the sunroof and lower the windows slightly.

2. I added a resister in the OAT sensor circuit so it can be switched into series with this sensor in the wintertime and prevents the A/C compressor from operating below about 47F OAT.

3. I added a switch in the panel just above my left knee to switch a resister into the cabin temperature sensor circuit so the computer will think the cabin is extremely cold. ANYTIME I need the defrost/defog/demist function I activate this switch just before I activate the defog function, the blower speed will be increased automatically as will the system HEATING level (to the windshield).

4. I installed a set of exhaust fans at each end of the exit airflow channel (at the rear of the package shelf) inside the trunk, 12 volt muffin type, two in each quarter panel to extract the air from the cabin whenever the rear window defog function or the windshield defog function is activated.

In my 2001 AWD RX300 I simply removed the A/C compressor clutch relay and put a small piece of black electrical tape over the blinking (indicates compressor failure) A/C indicator.

If I need defog function in the RX a simple "flick" of the temperature setpoint control **** brings it to max heat quickly and then I actiavte the defog function. The sunroof gets opened each and every night.

Canadian LS430s get electrically HEATED windshields, I guess Lexus assumes that the adverse wintertime climate conditions do not exist south of the canadian border.

 

wwest,

Too much information for one reading , I got to re-read this again.

Thanks for the info.

 

WWest,
Thank you so much for your input and relating your personal findings with the climate control system that we have. What I have noticed in my SC is that on cold mornings, the SC heater will really pump out alot of hot air and then diminish to a trickle. At times it will actually get cold in the car unless I turn up the heat from 70 to say 73 then the fan will increase speed and the system will pump more hot air in.

You seem to have made some interesting system modifications with the switches and fans and resistors and what not. I have not had the misfortune to have the fogging issue at all, I am glad to say.

I have had the funky, mildew like smell swack me in the nose in the end of the summer. It seems the air conditioner just leaves moisture in there. I have somehow disquised this by spraying Lysol Linen Scent into the fresh air vents just near the windshield wipers. This can sometime either eliminate the smell for perhaps 1 or 2 days.

I hear there is an exchange plenum heater that could be added in the aftermarket to get rid of the smell. It would dry out the exchange area. I have not gotten to that phase yet.

I have no problems with this smell in the fall or winter or spring. I sometimes wonder if something is clogged up in there???

 

I would have to say that the HVAC in my Lexus is second to none in terms of dehumidifying in cold weather. Every other car I've owned just hasn't cycled the compressor long enough in cold weather to get all the moisture out.

WWest,
The problems you're having will happen in any car that uses R-12 or R-134a, in those conditions. I cannot keep my windows clear when its in the 40s and raining unless I use the compressor... there's just too much moisture in the air.

 

Willard, thanks for all the info. I, like Art, have never had a problem with fogging, and I also only get that smell in the summer, I thought it was mildewy climate ctrl filters, but yeah, there must be accelerated growth in the system during humid weather, i'll have to follow Art's suggestion of spraying some Lysol in the cowl vents (Linen? you sissy mary). Interesting, the mods you've made to the system, you take your climate ctrl seriously. I think it's just not humid enough by us for the condensation to become a major issue as it normally would. Oh, and I agree with Red93sc400, it's irritating to put the system on max hot and have the compressor kick on and raise the idle, it's actually moved me forward towards the car in front of me at a light a couple times if I wasn't on the brake hard, plus I don't like the idea of having the compressor clutch engaged if I want to do a little spirited driving (needs all the hp it can get), so I turn it off, which is anoying since my CVA is in the way and I have to close it to do so. I've always considered modifying the system to alleviate that, but I do see the purpose, and I guess I would be creating one problem as I solved another.

 

The Lysol Linen scent is perhaps one of the most pleasant for the car. (I have tried them all). This all started when I put two sets of wet golf clubs and bags in the trunk. It got funky. Sprayed it down and dried it out. Then the next day, the inside of the car had a wonderful fresh aroma. Somehow the fragrance came into the cabin from the trunk.

Been using it ever since. I also have a bag of zeolite chrystals in the car under the passenger seat.

 

There is an aftermarket device that will help to remove the remaining moisture "trapped" on the evaporator vanes after the car is shut down. You can find it at

http://www.airsept.com/eed.html


The way it works is it runs the existing blower motor on an intermittent interval basis for a period of time after the vehicle is shut down.

I have heard one complaint that it didn't work very well but that was in a Lexus and I suspect that the exhaust air outlets in our Lexii are so restrictive that it couldn't work, just moved the super saturated atmosphere into the cabin but not out of the car.

Raising the temperature to combat cooling airflow in the wintertime...

My own experience has been that as soon as the system approaches the new higher setpoint it once again goes into cooling mode. My solution has been to over-ride the auto air routing and "freeze" it in footwell mode.

And by the way, that cooling airflow can be as much as 20F below your temperature setpoint according to Lexus. Nippondenso has a whitepaper that I have seen on the internet wherein they seem to very proud of their "Bi-level" airflow, cool dry airflow distributed in the upper part of the cabin "balanced" with warm airflow distributed from the lower outlets.

That's supposed to keep the windshield and windows from fogging up so readily but in my opinion it is extremely discomforting and obviously doesn't work for the purpose designed.

A/C indicator "on".

Is meaningless in the early models. Once the OAT declines below the shutoff setpoint you can depress the button and the light will come on but the compressor will not.

In the later models Lexus uses the evaporator downstream outlet sensor to determine when the compressor should be cycled off.

 

I am absolutely not opposed to the use of the A/C to help defog the windshield and keep it defogged, that technique has worked, and worked very well, for many years now.

Up until about the mid-eighties the A/C "technology" was such that running the A/C for this purpose was needless below about 47F, the additional efficiency needed to bring airflow below this temperature down to its dewpoint simply wasn't there.

So almost all systems of that era used additional heating brought "on-line" when defrost/defog/demist was activated. using HEAT will work for this purpose all the way down belwo sub-zero temperatures.

Then someone, I suspect an engineer at NipponDenso (Denso USA), decided that the efficiency could be extended and the A/C then used all the way down to the absolute minimum, 32F. The A/C evaporator cannot chill and dehumdify the airflow below this temperature without freezing the moisture and completely clogging the airflow.

They did this primarily by making the evaporator heat exchanger very very effiicent, and restricting the exhausting airflow from the vehicle to a very low level wherein the blower motor, once the cabin temperature setpoint was reached, could run VERY slowly.
The longer it takes for an air mass to move the the evaporator core the colder it will become.

But...

That very dense and complex evaporator dramatically increases the level, amount, of moisture left on its 10,000 square inches of surface area after the system is shut down. And we end up with a damp dank area that in the right overnight temperature range becomes the perfect breeding ground for the many forms of mold and mildew that exist everywwhere.

TOXIC mold? Maybe.

The A/C evaporator in my 92 LS400 was coated with an anti-microbe chemical which was supposed to eliminate mold growth. How long did this chemical last?

The other problems with that additional "surplus" leftover moisture is the early morning windshield fogging effect and the problem of sudden unexpected windshield fogging sometime after the A/C compressor is shut off.

There is only one place for the leftover moisture that doesn't "drain" away to go, into the vehicles cabin.

I'm currently looking into some way to mount a UV light source within the A/C evaporator plenum of my 2001 AWD RX300, and my 2000 GS300. The RX will soon have an exhaust fan mounted within the driver side rear quarter panel.

 

Well,

Almost all of japan is south of the 40th parallel (warm) and all of England and much of Germany is north of the 60th parallel (COLD).

Do you suppose this might be why the defrost/defog/demist systems on vehicles of european origin almost always work and those of Japanese origin almost always do not?

When I activate this function in my 911/996 I always get hot airflow to the interior windshield surface regardless of interiro or exterior climate or temperature circumstances. The A/C compressor does switch on simultaneously but its clear that the major contribution to the removal of condensation is the HEAT.

 

That makes sense but then again, parts of Japan do get snow.