Fresh air button causes drop in airflow?

In this 1990 Accord, when the Recirc button is pressed, airflow is good. No
problems.

When I push the Fresh Air button, the airflow coming out of all vents drops
about 20 percent.

I looked under the hood at the intake where the fresh air comes in, but
there's no removeable cover to be able to check for debris (leaves, etc.).

Anyone else experience this? Cause? Fix?

Is there a climate-control filter on this car?

Thanks,

 

Recirc opens a little door just above the right seat passengers feet and
recirculates the air from inside the car rather than drawing from outside.
When you switch to fresh, it closes the little door and opens the passage to
bring in outside air through the inlets at the base of the windshield. A
side effect of this is a reduction in fan noise because the fan is very near
the recirc door. It is possible that the air inlets are clogged with
debris, but usually it is just the change in fan noise that gives the
illusion of reduced air flow.

 

Recirc opens a little door just above the right seat passengers feet and
recirculates the air from inside the car rather than drawing from outside.
When you switch to fresh, it closes the little door and opens the passage to
bring in outside air through the inlets at the base of the windshield. A
side effect of this is a reduction in fan noise because the fan is very near
the recirc door. It is possible that the air inlets are clogged with
debris, but usually it is just the change in fan noise that gives the
illusion of reduced air flow.

 

That's normal. The airflow path is shorter in recirculation. An
interior vent opens up right at the fan inlet. The fresh air path is
in through the exterior vent, past rain deflectors, into the climate
control, out around the back seat, and then out through an exterior vent
under a fender.

 

That's normal. The airflow path is shorter in recirculation. An
interior vent opens up right at the fan inlet. The fresh air path is
in through the exterior vent, past rain deflectors, into the climate
control, out around the back seat, and then out through an exterior vent
under a fender.

 

That's right. To prove that the flow drops simply because the
resistance to inward airflow increases with the setting at "Fresh,"
simply feel the effluent and then lower a window. The flow should
then instantly increase to almost exactly equal the flow of
"Recirculate." If it doesn't, then there is something wrong, but the
condition as stated by the original poster is perfectly normal.
Ron

Ron

 

I don't have a 1990 Accord, so there may be something different about
it. However, this has not been my experience with other cars. In fact,
at cruising speeds, I find the flow often increases with outside air.
As someone pointed out, the fan is quieter which sometimes gives the
illusion of less airflow. I've never had any experience that would
suggest that the fan is trying to "suck in the outside air" as another
poster put it. With current flow through systems, air is drawn into
the car by the air exiting from the rear vents. At low speeds or
stopped, of course, the flow decreases and the fan becomes more
important.

If you are really interested, try taping a strip of paper or something
similar onto one of the vents. Make it long enough that it stands out
fair straight when you have the recirculating on. Then switch to
outside air and see if its position changes.

 

I don't have a 1990 Accord, so there may be something different about
it. However, this has not been my experience with other cars. In fact,
at cruising speeds, I find the flow often increases with outside air.
As someone pointed out, the fan is quieter which sometimes gives the
illusion of less airflow. I've never had any experience that would
suggest that the fan is trying to "suck in the outside air" as another
poster put it. With current flow through systems, air is drawn into
the car by the air exiting from the rear vents. At low speeds or
stopped, of course, the flow decreases and the fan becomes more
important.

If you are really interested, try taping a strip of paper or something
similar onto one of the vents. Make it long enough that it stands out
fair straight when you have the recirculating on. Then switch to
outside air and see if its position changes.

 

The fan speed drops is because its harder to push air into a sealed
container, like your car. Open your window a little bit, and it will blow as
much as the recirculation position. The reason it cools better on
recirculation is due to the fact that the air is already cooler than the
outside air, and usually less humid. Also blows more air cause there is no
resistance to flow.

 

The fan speed drops is because its harder to push air into a sealed
container, like your car. Open your window a little bit, and it will blow as
much as the recirculation position. The reason it cools better on
recirculation is due to the fact that the air is already cooler than the
outside air, and usually less humid. Also blows more air cause there is no
resistance to flow.

 

I think what you are perceiving as a slow down in fan speed
is more likely the difference in the sound you hear, when the
recirculation door closes and the exterior access door opens,
muffling the louder sound the fan produces when in recirc
mode.


mike hunt

 

I think what you are perceiving as a slow down in fan speed
is more likely the difference in the sound you hear, when the
recirculation door closes and the exterior access door opens,
muffling the louder sound the fan produces when in recirc
mode.


mike hunt

 

I appreciate your contribution to my search for an answer, but please believe
me. I am not simply "perceiving" differences in sound.

I can only attribute this to the increased path through the air intake, and
possibly debris at the climate control air intake.

Thanks,

 

I appreciate your contribution to my search for an answer, but please believe
me. I am not simply "perceiving" differences in sound.

I can only attribute this to the increased path through the air intake, and
possibly debris at the climate control air intake.

Thanks,

 

Wow! Really? Gee Mike...your a genius!

 

Wow! Really? Gee Mike...your a genius!

 

The speed of the fan is not related to the recirc setting. It is
louder for reasons already covered by others. You may find cracking a
window increases flow and your perception of the speed of the fan.

 

The speed of the fan is not related to the recirc setting. It is
louder for reasons already covered by others. You may find cracking a
window increases flow and your perception of the speed of the fan.

 

Cars are not sealed containers. They have specific outlets to enable a
controlled flow of air through the car. They do have a bit of positive
pressure, presumably to enhance heating and cooling and to lessen
drafts within the car.

 

Cars are not sealed containers. They have specific outlets to enable a
controlled flow of air through the car. They do have a bit of positive
pressure, presumably to enhance heating and cooling and to lessen
drafts within the car.