1972 240Z Blower Ducting

[52crankman]

I am reconditioning all of the ducting and am curious why the ducting for the front vent uses foam weatherstripping on the inside .  I do not see how this is useful.  Anybody know the reasoning for it.  See picture.

[Zup]

My initial thoughts---

To buffer temperatures of the cold air to metal contact, hence sweating (condensation) during periods of high humidity.

Since the foam used was not closed cell, it would also effectively become a sponge for some of the condensation if it occurred.

 

[grannyknot]

It's to feed the mice that will eventually make their home in the heating system

[Namerow]

9 hours ago, 52crankman said:

I am reconditioning all of the ducting and am curious why the ducting for the front vent uses foam weatherstripping on the inside .  I do not see how this is useful.  Anybody know the reasoning for it.  See picture.

It's a form of 'acoustic duct lining' and it's there as an airflow silencer.  Not sure how effective the end result is.  You'd need to try a the system 'with' and 'without' to decide.

BTW, I did this same job myself a couple of years ago.  It's very time-consuming.  There are a lot of foam gaskets in the Z's heater/blower/vent/duct system and some have very tricky shapes (esp. the piece in your photo).  Many need have holes punched out for joint fasteners.  Rather than use contact cement to try to glue new foam in place (messy), try making your own adhesive-backed foam by bonding the foam to two-side-adhesive-backed clear vinyl sheet (8-1/2" x 11" -- available at craft stores).  Leave the peel-off paper in place on one side of the vinyl sheet.  Now draw your gasket templates onto a piece of 8-1/2" x 11" printer paper and use a glue stick (stationery supply store) to glue the paper to the vinyl backing sheet.  Now you can use a razor knife, scissors, hole punches, etc. to cut out your gaskets.  When done, peel off the backing sheet from the vinyl-backed foam and stick in place.

Most of the gaskets should be about 1/16" thick, installed.  I used 1/8" open-cell foam (compresses down to 1/16"), but I think some craft stores sell adhesive-backed, closed-cell neoprene sheet in 1/16" thickness that might be an equally good .  Don't use the 1/4"-thick adhesive-backed foam 'tape' that hardware stores sell for home weatherstripping.  It's too thick and the end results I've seen in photos look pretty marginal.

The foam covers for the two big 'flapper' doors need to be top-faced with thin, upholstery-type vinyl.  If you don't do this, the foam will wear off quickly around the perimeter, where it seats on the ridge in the housing.

The gasket that's the most difficult to get right is the one around the perimeter of the heater plenum, where the removable end plate installs (for access to the heater matrix).