willard west

My new 1992 Lexus LS400 came to me with a special Lexus "feature", one that to my knowledge I had never encountered before.

The air conditioning evaporator, heat exchanger, was coated with a fine porous nylon film into which was embedded an Anti-microbe chemical.

Apparently it was an effort by Lexus to eliminate or at least retard the growth of mold and mildew spores in the damp and dank environment of the A/C plenum area containing the complex and dense evaporator structure appropreate to a luxury sedan.

Over the past ten years I have noticed a great number of posts on various automotive forums on the internet complaining of a "musty smell" or the "dirty sock syndrome" emanating from the vehicle's A/C outlets. There also seems to be a great number of posts regarding the frustration of dealing with windshields that suddenly fog up or cloud over, especially in the early morning. I myself have been VERY frustrated over owning various Lexus models over the years, Bill Gates' 90 LS, my 92 LS, a company 95 LS, a 2000 GS300, a 2000 RX300 AWD and a 2001 RX300 AWD. ALL having the propensity to spontaneously, completely and totally unpredictably, suddenly fog over the entire interior windshield surface.

Just recently I noticed an aftermarket product designed to combat the formation and growth of mold and mildew in the automotive evaporator plenum environment. It's description and purpose is worth a read...

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

But how do you go about eliminating the mold (possibly even TOXIC mold) and mildew growth and eliminate the extremely hazardous circumstances of windshield fogging, spontaneous are simply repetitive early morning occurances?

My recommended solution to you Lexus owners is much less expensive to implement and will take about ten minutes of your time twice a year.

As wintertime approaches, once the average overnight outside temperatures have declined below about 55 degrees F, remove the A/C compressor clutch control relay and store it away for safe keeping to be reinstalled the next spring when the actual need for A/C cooling returns.

The A/C indicator on your dash will flash on and off, indicating that the A/C compressor is not turning in synchronization with the engine. You can use that flashing as a reminder to reinstall the relay when the time comes, or you can cover it with a small piece of electrical tape if it annoys you.

With no moisture (well, virtually none) being accumulated on the evaporator vanes during the cold winter months when it will not readily evaporate away during the night, you will not have need to worry regarding mold and mildew growth.

And guess what?

A REAL bonus, there will be NO "surplus" moisture available to coat the interior surface of the windshield when you first start the vehicle up in the cold early morning hours.

AND... You are now free to use the defrost/defog/demist function without fearing the return of the dreaded moisture TIME BOMB.

If the A/C compressor were working in this mode it would cause a great deal of moisture to be accumulated on the dense and complex evaporator surfaces and now you would be TRAPPED in the defrost/defog/demist mode FOREVER. Or at least until you can somehow remove the condensed moisture from the thousands of square inches of evaporator surface without having it evaporate back into the incoming airstream and start the initial defrost/defog/demist process all over once again, and again, and again.....

Now you will rarely have need to defrost/defog/demist the interior surface of the windshield or windows. But when you do the proper procedure will be the old time tested , and well proven one, activate the defrost mode, but simultaneously turn up the heating setpoint to lower the relative humidity enough to accommodate a "state change", the moisture condensed onto the windshield is in a liquid "state" and you need to "boil" it off, change it to a gaseous "state".

In a Lexus, once the cabin atmosphere has acclimated to the system setpoint, say, 71 degrees F, the climate control system airflow temperature to the interior surface of the windshield temperature level will be, predominantly, about 66 degrees F, and with four full grown passengers it might be as low as 50 degrees F. When you switch the mode to defrost/defog/demist, there is NO input to increase the airflow temperature level to the windshield, so you must do this manually.

The old saw, "An ounce of prevention is worth a pound of cure" still holds true.

Lexus correctly uses the A/C compressor, "an ounce of prevention" to PREVENT fogging of the windshield, but they neglected to remember the "pound of cure" once the windshield condensation is fully formed as a result of the windshield itsself having been CHILLED to the dewpoint of the surrounding atmosphere.

Once condensation has formed on a cold interior windshield surface it will take more than a "pound of cure", it will take something on the order of a "sledgehammer" to force a "state change" in the chilled liquid held to the windshield by its own viscosity.

HEAT!

tmsiegel

Just a little info on your AC mildew and smells.

1 Cause clogged AC drain tube.
( Repair ) have it blown out that will keep the mildew out.
2 You must leave the AC functional, That is what keeps the window defogged it dehumidifies the window, That is How it was designed by removing the AC clutch relay will only make it worse.

willard west

my post is, but please read it in more detail.

The mold and mildew grows in your A/C plenum due to darkness and dampness. Most of the water " sucked" out of the air to keep the windshield from fogging does flow out the drain tube, but not nearly all of it.

In the summertime when the overall ambient tempertaure is fairly high any moisture left in the system will likely evaprorate away overnight, in the wintertime not!

tmsiegel

I disagree, I Have opened atleast 100 or better units and the only stuff we find in these evap housings are dirt leaves and all kinds of debri and the unit is designed that most if not all the water to drain out, and the evaperater is also insulated with foam. The only vehicles we find that smell or dont clear up are the ones that are clogged.

P.S disconecting the AC is not the correct prcedure for correcting this concern.

willard west

The 92 Lexus LS400 A/C evaporator has almost 10,000 square inches of evaporator cooling, heat transfer, surface, within a 4X20X18" space, approximately 80% of that is horizontally oriented, 50% top, 50% bottom vane surfaces.

If you could take one of these, use it for a day here in Seattle's humid sub 60 degree F weather, then park it overnight in an unheated space, I would bet good money you would find enough moisture left on it the next morning to coat ten LS400 windshields to a level wherein forward visibility would be virtually zero.

If you could see that mold and mildew growing then would you please explain to me wust what you think you would see.

They aren't called microbes for nothing.

And if you think this isn't a serious issue then browse around on the internet for the number and variety of products in the marketplace being produced speciifcally to combat the mold and mildew problem, smell, dirty sock syndrome, coming form many modern automotive A/C vents.

Did you follow the link to see the Airsept EED? Do you think they have developed and are manufacturering this product for a market that doesn't exist?

tmsiegel

I understand the concern about mold and mildew and the health issues it causes and i have delt with this concern before with a few sensative customers, And I dont disagree that lexus as well as many other manufactures have this concern. But the reason for my first reply is for a proper repair and or correction to this concern.

willard west

Once you shut down the A/C compressor, how do you safely and correctly remove the moisture that remains on the evaporator surfaces?

My initial answer was to leave the sunroof and windows slightly open in the garage at night.

Since it is clear to all that the A/C cannot be used to remove or prevent windshield fogging when the air temperature is near or below freezing, what is your recommended solution?