Piper Archer II Air Leak Problem by Back Seat.

Piper Archer II PA28-181
Help please !!
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.
The cold air flow with the overhead duct closed must be coming from central
air outlet under the belly of the bird ?
We never had this problem before the new air duct was fitted ?

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 ?

Thanks for all input.
--
Roy
Piper Archer N5804F

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