Thanks Jay,

Unusually, I did not replace the upper air duct myself so I did not have the
chance to see the rear flapper valve.
I do know that the valve works effectively because when the operating knob
is pulled out to the off position all fresh air stops coming out of the 4
overhead ducts.

Now I am making an assumption that when the overhead duct is on, the cabin
is very slightly *pressurized* which stops the flow of up coming in from the
belly open duct.
The back seat set up in my Archer will be very similar to your Pathfinder, a
pair of seats which mount on the removable floor board which itself has a
vent each side.

I have been involved for several years assisting with annuals and fitting
new interiors to PA28-180/181 aircraft so I am very familiar with taking out
the floor boards etc.
I now do all of *preventative maintenance* that the rules allow on my own
Archer so frequently get to see the innards of the beast.
The centrally mounted belly vent, as you say has no valve, the external
shield should work a bit like automatic bailers fitted in racing sailing
dinghy's.
By hanging down in the breeze, it should create some "suck" and pull stale
cabin air through the rear board vents into the outside world.
But it does appear that when I close the overhead duct, I am getting a
reverse flow from under the rear seat board back through the board side
vents into the cabin.

At the time of fitting the new overhead plastic ducts [November] my shop did
several other jobs, namely I had them re-rig all the flight controls and
replace a couple of smoking rivets.
The issue with the draft appeared immediately after that spell in the shop.
The bird is booked into the paint shop in Feb and I am trying to make sure
that all is good before getting stripped and painted.
[In fact this week the shop is fitting gap shields and wing root fairings]

During December I had a new leather interior fitted, so the fit of the seat
board against the wall panels is now very snug.
But still the howling draft pours through the right side seat board vent.
I wonder why no draft out of the left seat board vent ?
That might be the key to solving the issue !

Roy




"Jay Honeck" wrote in message
ps.com...
We have just replaced the cabin roof airduct in our 1977 Piper Archer II
PA28-181.
The duct feeds fresh air from the rear mounted blower to each of the 4
overhead air outlets.
The air is controlled by a push & pull cable mounted in the duct.
With the air duct closed, no air being fed to the overhead ducts, there
is
howling cold airflow up through the right side of the rear seat floor
duct.

Having spent a goodly amount of time working on (and replacing) that
very same fresh air flapper (the one that controls the ceiling ducts)
in my '74 Pathfinder, I can tell you without hesitation that it has
NOTHING to do with the air coming in the floor ducts.

If air is coming out of a floor duct, you've got a bad flapper valve in
that duct. Make sure to check that the cold air isn't actually coming
from under the back SEAT.

If you have the bench seat, this is an extremely common place for air
to leak into a Cherokee. Luckily, it can be easily remedied with a
strip of strategically-placed closed-pore foam insullation, laid down
where the bench seat meets the bottom of the airframe.

This 75-cent piece of foam can make all the difference in the world.

The cold air flow with the overhead duct closed must be coming from
central
air outlet under the belly of the bird ?

Nope. However, there IS an inlet on the belly that could be the source
of air leaking under the seat. This inlet on the bottom of the plane
is simply an open hole -- there is no control.

Our maintenance crew have had both the overhead duct system apart and the
rear seat board out to inspect that area.
Everything looks normal and they are perplexed how to cure the problem.
I wonder how many other PA28 owners with overhead fresh air ducts have
had
this issue ?

I spent a dozen or more hours weather-sealing my old '75 Warrior. It
was colder than hell in the winter, and my poor kids had to fly wrapped
in a sleeping bag in winter. After methodically sealing the door, and
each leak (Example: Stuff "Nerf" balls in the floor ducts to really
seal out any leaking air), we could fly that plane in shirtsleeves, no
matter what the weather.

Good luck!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"