I have an 06 EX, no nav. During AC season I like to run the fan full blast for a few minutes before turning the car off to prevent that AC mildew and smell that AC causes. It looks to me like I have to 1. hit the fan-up button a few times to turn off the "auto" feature and get the fan turned up full, 2. hit the AC Off button to make sure AC is off and 3. Hit the button a few times to get it to where it shows air through the vents and air to the feet (to ensure it is in "fresh air" mode. Is this correct? If I simply hit the fan-up button will that automatically turn AC off an put me in fresh air mode? The reason I don't think so is that the AC-Off indicator does not turn on in the display when I do this, and it feels like the air is still cooled.

When the HVAC is in Auto mode, the computer controls the air vent output, AC on/off, fan speed and recirculation for optimal heating/cooling. The only way to bypass the HVAC computer is to hit every button that controls the HVAC other than the Auto and Off buttons. For example, if the system is in auto and you hit the mode button, the HVAC computer will still control the recirculation, ac and fanspeed.

You could hit the AC button to turn off the compressor, turn the temp knob to Lo then control the fan by hitting the up and down arrows, but most of this is unnecessary. The HVAC filter does a pretty good job of preventing mold and mildew from forming in the HVAC ducts.

On a similar note...does anyone know how to use the windshield defogger without firing up the A/C unit? Last time I drove home in terrible rain, my windshield would fog near completely, and if I hit the windshield defog button it would clear it within a few sections. Now I've never had a climate control system in a car before (sunfire was manual everything), so I used to just crank the fan up to full, heat set to full (or cold set to full, depending on time of year) and then set it to blow out the windshield vents. I've tried to do this in the accord (temp set either quite high or at "lo", AC off, fan max, air routed to windhield and at feet), and although it does clear somewhat, its nothing compared to what the HVAC computer can do.

Anyone know how to emulate what is does without using the A/C? My main reason for this is that I don't need the A/C during most of the year, and really don't want the added gas consumption of running the full A/C system just to keep my windows clear...

Thanks in advance.

There's really no way to clear a windshield that quickly without AC. AC takes a lot of moisture out of the air, so that's what makes up the difference...you're not blowing "wet air" onto a damp surface, you're blowing "dry air"

The system uses inside air when in the recirculation mode & outside air if it's not. No matter how high you have the fans it will only get the air from inside or out depending on which mode it's in. The fan speed will do nothing to prevent moldy smell. Making sure the last mile or so it's on fresh air before garaging it is the best bet.

When parked in the heat it will automatically go to recirculation & high to cool it off faster, then if you have it set on auto, it will go back to fresh air by itself. Mine's always on fresh unless passing something stinky!!! (there's a stretch on I-5 with a bizillion cows near Coalinga....P-U) At a light behind some Fords will also force me to hit that button too!

Yep, the AC runs when defogging...that's what takes the moisture out. That's when the evaporator works.

You should run the AC at least 10 minutes every other week to lube the compressor and condition the seals even if it's not "AC season". (yes. that includes freezing weather, too) Just turn up the heat if you have manual AC or set the auto AC a few degrees higher and you'll be fine.

There's really no way to clear a windshield that quickly without AC. AC takes a lot of moisture out of the air, so that's what makes up the difference...you're not blowing "wet air" onto a damp surface, you're blowing "dry air"
Another way to look at it is, if you blow air from your lungs (warm, moist air) onto a cold piece of glass, the glass will fog up. If you take that piece of glass and place it in front of the AC (cold - but not freezingly cold - dry air), the fog will clear up. If you heat the piece of glass with a hair dryer (hot air, with AC off), it will be harder to make the fog "stick".

The system uses inside air when in the recirculation mode & outside air if it's not. No matter how high you have the fans it will only get the air from inside or out depending on which mode it's in. The fan speed will do nothing to prevent moldy smell. Making sure the last mile or so it's on fresh air before garaging it is the best bet.

When parked in the heat it will automatically go to recirculation & high to cool it off faster, then if you have it set on auto, it will go back to fresh air by itself. Mine's always on fresh unless passing something stinky!!! (there's a stretch on I-5 with a bizillion cows near Coalinga....P-U) At a light behind some Fords will also force me to hit that button too!

Yep, the AC runs when defogging...that's what takes the moisture out. That's when the evaporator works.

Ok so what happens in the winter when the window fogs...you wouldn't want the compressor running in below 0C/13F weather...

it wouldn't kick on anyways..... i tried it already......

since the air is already below freezing, the A/C compressor would not kick on in that case.

It's safe to run the AC in freezing temps down to about -10 degrees C (about 15 degrees F). Any temp below that and you should be able to use the AC safely after the engine's been running for about 20 minutes. The cold weather doesn't affect the compressor, but it will affect the refridgerant.

The compressor doesn't run automatically when you split the air between the windshield and the floor (use the mode button to pick the right setting).

You could hit the AC button to turn off the compressor, turn the temp knob to Lo then control the fan by hitting the up and down arrows, but most of this is unnecessary. The HVAC filter does a pretty good job of preventing mold and mildew from forming in the HVAC ducts.

Yes, that is essentially what I am doing. I guess I was hoping for an easier way. Not that big a deal though.

On a similar note...does anyone know how to use the windshield defogger without firing up the A/C unit? Last time I drove home in terrible rain, my windshield would fog near completely, and if I hit the windshield defog button it would clear it within a few sections. Now I've never had a climate control system in a car before (sunfire was manual everything), so I used to just crank the fan up to full, heat set to full (or cold set to full, depending on time of year) and then set it to blow out the windshield vents. I've tried to do this in the accord (temp set either quite high or at "lo", AC off, fan max, air routed to windhield and at feet), and although it does clear somewhat, its nothing compared to what the HVAC computer can do.

Anyone know how to emulate what is does without using the A/C? My main reason for this is that I don't need the A/C during most of the year, and really don't want the added gas consumption of running the full A/C system just to keep my windows clear...

Thanks in advance.


On cars with A/C, the BEST defrosting/defogging is done in the completely automatic mode... That is simply, turn on the defroster. The A/C dries & dehumidifies that air that will be blowing onto the windshield removing the inside fog/mist. Setting the temperature while in Defrost mode is ONLY a comfort thing. Its NOT the heat that's defogging the glass, but rather the dry air conditioned air.

On cars without A/C a high fan & high heat are required to do any defrosting at all. (How many times had you given up on that method of defrosting, and hurriedly wiped the inside of the glass?) Non A/C cars have virtually no defrosting ability. A/C'd cars will heep a windshield clear all by themselves when the A/C is on. Blasting it up to the windshield ("Def" mode) simply does it faster. Thats why most all car manufacturers have programmed the cars to turn on the A/C compressor whenever you go into the Defrost Mode, in ANY season, as long as the outside temperature is above about 25 degrees. The A/C compressor will cycle on & off depending on how warm you have the cabin temperature set. It is not on all the time.

You're not saving gas at all by turning the A/C off & opening the windows because you are making the wind blow thru the car & upsetting the wind dynamics of the car. (Assuming you don't drive the car like a crazy person.)

welcome aboard barry.... :wave:

to clarify, i beleive that this has been discussed before.... below 40mph, you'll get better MPG with windows down.... 40mph and above, a/c would be best..... :yes: :)

You're not saving gas at all by turning the A/C off & opening the windows because you are making the wind blow thru the car & upsetting the wind dynamics of the car. (Assuming you don't drive the car like a crazy person.)

Typically I just have the fans on high so they're blowing enough air to keep the cabin at my liking...also I might tilt the roof slightly, but thats pretty much it (wouldn't open windows at all in the rain...too much would come in).

A better way to keep that mildew smell away is to just run your AC full blast with the recirc off and spray Lysol for several seconds in the outside vent just under the driver windshield wiper. Do this once a month and you'll never smell the dew...

A better way to keep that mildew smell away is to just run your AC full blast with the recirc off and spray Lysol for several seconds in the outside vent just under the driver windshield wiper. Do this once a month and you'll never smell the dew...

Another way to prevent mold/mildew in the ventilation system is to turn off the compressor 5 minutes before shutting the car down.

If the ductwork is allowed to normalize to ambient temperature while air is being forced through them, there is less of a chance that moisture will condense on the warming surfaces (which is what happens if you park the car and the ducts are cold/dry on a hot/humid day).

If the re-circulation light is not on, then you are getting fresh air. Shutting of the a/c & turning the temp to LO will give you the highest fan setting without manually stepping up the fan speed.

Anyone know how to emulate what is does without using the A/C? My main reason for this is that I don't need the A/C during most of the year, and really don't want the added gas consumption of running the full A/C system just to keep my windows clear...
I'm one of those that keep my a/c off by default unless I absolutely need it, but when it fogs during rain, there really is no way to get around not using the a/c. What I do is set it to defrost first, then after the winddshield is clear, I set it to AUTO. This way the fans are not going full blast & the windows stay clear.