windshield defogger -- cool air in warm weather w/o A/C?

When the windshield defogger is operating in my 2003 Accord (on
a cool temperature setting), and the A/C is apparently off (the
A/C indicator lamp is unlit), I note that really cool air comes
out of the upper dash vents even in mid-80s weather. The air is
so cool, especially when the car's interior is not hot, that I
find myself not even needing to activate the A/C!

What is the source of this cool air? Is the A/C system actually
operating in tandem with the windshield defogger on the cool setting?

Paul

 

Yes it is. The purpose being to dehumidify the air.
Adjust the temperature setting to suit.



mike hunt

 

Yes it is. The purpose being to dehumidify the air.
Adjust the temperature setting to suit.



mike hunt

 

It actually is the reverse........use the recirc air button once the air is
cold inside the cabin......make the ac work less as it is recirculating
cooler air. Don't use the recirc button until the air is cool.....and open
the window for a few moments to have hot air escape faster

 

It actually is the reverse........use the recirc air button once the air is
cold inside the cabin......make the ac work less as it is recirculating
cooler air. Don't use the recirc button until the air is cool.....and open
the window for a few moments to have hot air escape faster

 

Actually you have it backward. One should run on fresh (outside)
air to pull in outside air and push out the hot air within, when
using Air conditioner. Once the vehicle begins to cool, go to
recirc to re-cool the dehumidified air inside the vehicle. There
is always an infusion of some outside air in any event. In the
defrost mode the air source is from outside. If you vehicle has a
manual recirc/fresh (outside) air controller, the recirc should
only be used for AC, not heating, or your will build up
humidity. Read your owners manual for complete instruction of
the operating of the HVAC system, WBMA


mike hunt

 

Actually you have it backward. One should run on fresh (outside)
air to pull in outside air and push out the hot air within, when
using Air conditioner. Once the vehicle begins to cool, go to
recirc to re-cool the dehumidified air inside the vehicle. There
is always an infusion of some outside air in any event. In the
defrost mode the air source is from outside. If you vehicle has a
manual recirc/fresh (outside) air controller, the recirc should
only be used for AC, not heating, or your will build up
humidity. Read your owners manual for complete instruction of
the operating of the HVAC system, WBMA


mike hunt

 

Good advice.
Mine says to open a window for sec to dump the hot air, and run the A/C in
recirc.
Even says to run in recirc for fast heating, but switch to fresh if things
begin to fog up.

1991 Honda Accord Owners Manual

 

Good advice.
Mine says to open a window for sec to dump the hot air, and run the A/C in
recirc.
Even says to run in recirc for fast heating, but switch to fresh if things
begin to fog up.

1991 Honda Accord Owners Manual

 

Whether you're recirculating air or not, your air conditioning system
is still working just as hard. Your air conditioner is either on or
off, there's no (or very little) difference in the amount of work
required. When you have your internal temperature warm or cold,
recirculating or not, you're AC system is working just as hard. The
only way to reduce the amount of fuel consumption is to not use AC.

If you know how air conditioners work, the COMPRESSOR compresses a gas
(R134 or equivalent) within the cooling system. It requires energy to
compress the gas, which is supplied by your engine (via a
belt/pulley). When this gas is allowed to expand, it gets very cold.
This entire cycle is contained within it's own system so that gas
isn't lost.

 

Whether you're recirculating air or not, your air conditioning system
is still working just as hard. Your air conditioner is either on or
off, there's no (or very little) difference in the amount of work
required. When you have your internal temperature warm or cold,
recirculating or not, you're AC system is working just as hard. The
only way to reduce the amount of fuel consumption is to not use AC.

If you know how air conditioners work, the COMPRESSOR compresses a gas
(R134 or equivalent) within the cooling system. It requires energy to
compress the gas, which is supplied by your engine (via a
belt/pulley). When this gas is allowed to expand, it gets very cold.
This entire cycle is contained within it's own system so that gas
isn't lost.

 

Nope. Open the windows and set to fresh air. Once the superhot air has
left the inside of the car, and the car is at outside temperature, close
the windows and set to recirculate.

You need to exhaust the superhot interior air before the A/C can really
do any good.

 

Nope. Open the windows and set to fresh air. Once the superhot air has
left the inside of the car, and the car is at outside temperature, close
the windows and set to recirculate.

You need to exhaust the superhot interior air before the A/C can really
do any good.

 

On Tue, 19 Aug 2003 20:24:41 -0400, "Elmo P. Shagnasty"

<snip>

Some homes have installed ventilation systems that will exchange
indoor air with filtered outdoor air at the rate of 350 cubic meters
per hour.

 

The interior of the car is what - 2-3% of the interior volue of your
house? Plus you have many materials in the car not usually seen in a
house. I don't think this is a very good comparison. There's also a huge
difference in how they're expected to operate, e.g., a house may take
hours to cool, whereas if the car isn't cold in 5 minutes, the %^&$$%^&
a/c is broken!

FWIW, everything I've read over the years has recommended opening a
window and running on RECIRC when starting up a car with a heated
interior, then closing the window and switching to FRESH. With the
windows (& moonroof, if present) closed, there isn't much fresh air
coming in, just equal to what the cabin vents permit to escape
(otherwise the interior would get pressurized and it would be like scuba
diving).

Finally, as the a/c compressor cycles on & off, it's consuming
significant power only when it's running. The fan runs constantly and
consumes *much* less power than the compressor.

 

The interior of the car is what - 2-3% of the interior volue of your
house? Plus you have many materials in the car not usually seen in a
house. I don't think this is a very good comparison. There's also a huge
difference in how they're expected to operate, e.g., a house may take
hours to cool, whereas if the car isn't cold in 5 minutes, the %^&$$%^&
a/c is broken!

FWIW, everything I've read over the years has recommended opening a
window and running on RECIRC when starting up a car with a heated
interior, then closing the window and switching to FRESH. With the
windows (& moonroof, if present) closed, there isn't much fresh air
coming in, just equal to what the cabin vents permit to escape
(otherwise the interior would get pressurized and it would be like scuba
diving).

Finally, as the a/c compressor cycles on & off, it's consuming
significant power only when it's running. The fan runs constantly and
consumes *much* less power than the compressor.

 

There's *always* outside air being brought in, even in recirculate. And
as for materials in the car, everything in a car is seen in a house.
The chemical makeup is no different--even the exhaust.

Speaking of, recirculate minimizes the exhaust you bring through the
car. That's why Japanese cars have the separate recirc button--Japanese
law requires it because of the exhaust and pollution issue. American
cars typically don't have such a button, because nobody ever made them
have one.

Have you ever read your owner's manual? What *have* you read that
recommends the above? It makes no sense, actually, to start out on
recirculate. You want to cool the car down quickly, which means drawing
in outside air--which is much cooler and therefore easier for the A/C to
cool even further--and exhausting the very hot trapped air.

Right, which is why you open the windows to allow the extra hot trapped
air to be blown out by outside 90 degree air being drawn in and much
more efficiently cooled by the A/C. The net effect is that the interior
cools down MUCH more quickly than if you asked the A/C to start cooling
the 140 degree interior air.

 

There's *always* outside air being brought in, even in recirculate. And
as for materials in the car, everything in a car is seen in a house.
The chemical makeup is no different--even the exhaust.

Speaking of, recirculate minimizes the exhaust you bring through the
car. That's why Japanese cars have the separate recirc button--Japanese
law requires it because of the exhaust and pollution issue. American
cars typically don't have such a button, because nobody ever made them
have one.

Have you ever read your owner's manual? What *have* you read that
recommends the above? It makes no sense, actually, to start out on
recirculate. You want to cool the car down quickly, which means drawing
in outside air--which is much cooler and therefore easier for the A/C to
cool even further--and exhausting the very hot trapped air.

Right, which is why you open the windows to allow the extra hot trapped
air to be blown out by outside 90 degree air being drawn in and much
more efficiently cooled by the A/C. The net effect is that the interior
cools down MUCH more quickly than if you asked the A/C to start cooling
the 140 degree interior air.

 

It controls a blend door, which introduces more or less heated air as
required. The A/C always runs the same.

 

It controls a blend door, which introduces more or less heated air as
required. The A/C always runs the same.