I used the front defrost on my '09 TCH and it seemed the air was very cold like the A/C was on but the A/C light doesn't show. I always hated the US vehicle way of requiring the A/C to turn on to defog rather than the Japanese way of making the A/C just an On/Off button independent of the air venting control.

Anyone know for sure?

 

Sorry, this IS the japanese way. Before Japan, in the form of NipponDenso (IDIOTS, ALL..!!), become dominant in the US automotive industry it was common, and sound, knowledge, that while A/C could be of help in defogging/demisting the interior surface of the windshield it often was NOT. So american automotive HVAC manufacturers always used HEAT combined with the A/C. If the A/C didn't work, as often mother nature dictates, the HEAT did.

My A/C gets SWITCHED OFF (disconnected, c-best option, etc) in the fall and doesn't get switched on until the first time I actually need cooling the next spring.

 

Why?????????

 

1. AC will remove some moisture from air, by the nature of physics where colder air can not hold as much water, so it should be helpful with defrosting and especially defogging the windshield.
2. Not using AC for long time will make it fail sooner. I think it says something like that in manual, not sure, anyway just the only sensible way for AC to be turned on in winter, spring and fall would be defroster. The only reason one could object to AC running sometime in winter would be fuel economy? Now, fixing AC is rather expensive. My father spend hundreds of dollars to get his working when it broke few years back and I end up, fixing it again year later this time for good by replacing slowly leaking radiator. Now cost of fixing AC is much, much higher than any gas savings form not running it at all in cooler weather, so I leave mine alone. As a matter of fact I run it on purpose once a month or so for few min. just to get oil inside to circulate etc. I don't use AC often but sometimes you just cant' be without and I want to have it when really needed.

 

yes....I agree with most of this.....What I am wondering is why wwest turns his off????? Maybe he is refering to his Lexus, and not a camry hybrid.....

 

NONE of my cars will ever have the A/C compressor enabled during the cold weather season. My history of that only goes back to '68, ~250k miles on a Ford station wagon, so I can't really say about any long term damage to the system.

Windshield fog/mist..?? Turn the HEAT up to HEAT the windshield, ALWAYS works, ALWAYS.

In order to improve the efficiency of automotive A/C the evaporator cores are very tightly "woven", much like a sponge when it comes to retaining moisture for days once used just briefly. Results: mold and mildew odor, horrid odor. Instances of sudden windshield fogging, HAZARDOUS instances, when the retained moisture is for some reason or another released to flow into the cabin.

 

I drove my old Nissan to junk yard somewhere after 250k miles, can't tell exactly since odometer wasn't working reliably, after 2nd tranny failure. AC on that car was colder at the end of it's life than on my brand new replacement car. Never had a problem with mildew or bad smell and the trick here is to not use AC right before the end of trip, basically close to my destination I shut off AC and just run fan for few min. to dry everything up. In colder weather that's not even an issue me think: 1) mildew doesn't prosper too well in cold weather 2) Most likely the heat would be on and dry everything up 3) once the cabin is all warmed up, I usually would have no need to run defogger/defroster anyway, unless the weather is really bad and that means moisture is everywhere no matter what. Anyhow, if it works for you, why not? I never had a problem either.

 

Older vehicles, say pre-mid-eighties, were not so design sensitive to/for FE. Look at the cooling vane/surface density of a 1980-ish A/C cooling evaporator vs a 1992 or later one as an example. Additionally the older systems would shut down, automatically switch off due to rising head pressure with lowering OAT, typically 45-50F.

THe newer systems are designed to operate all the way down to ~35F where the electronic systems force a shutdown.

The net result is that the newer systems operate more often in a region of questionable efficiency insofar as dehumidification is concerned. And then drive one of these from a reasonable warm, >40F, and humid climate and into a cold region, <35F, and you'll be putting your life in serious danger.

And by the by when you shut down (yesterday, or exiting defog/demist) one of these new systems, or it shuts down of itself automatically, there will be as much as a pint or two of moisture left "trapped" on the ~10,000 square inches of evaporator cooling vane surface area.

 

I provide the following scenario when it WON'T work, and I have personally experienced this.

It was a cool rainy day, say 45-50 degrees. The A/C hadn't been run in the car in several months. (NO, not even the defroster!) Three people walk from whatever building they have been in, their clothes getting wet from the rain, and enter the car. The car has been sitting for several hours so the engine is cold. Start the car, turn on the wipers and the HEAT, and all windows fog up, almost immediately. I resist using the defroster (A/C) for several reasons. (hey, it uses more fuel to run the A/C, and it's COLD outside, why use it?) As the engine slowly heats up, so does the temperature of the air blowing out of the HVAC system, but the windows remain fogged. I finally decide this is crazy, and turn on the defroster (A/C) with the temp set to a warm setting, and the windows un-fogged in less than a minute. I am now able to drive away.

Perhaps in your neck of the woods this isn't possible, as it is always damp and humid there, but that has happened to me on more than one occasion here in the desert SW, and I suspect that others have experienced this as well. I will continue to use the defroster (A/C) to defog my windows.

 

You probably could have accomplished the same effect by lowering the rear windows slightly and making sure the system was taking in FRESH outside cold airflow and exhausting the HEATED and HUMID cabin air.