RE: Rear Heat Exchanger 1972 Squareback

["Rik Ponne" <rikponne@gmail.com>]

My 67 square also has all of its heating stuff removed long ago (by a
previous owner). Now, considering my location (Thailand), I really don't
need any additional hot air entering my cabin than that is already coming in
from outside and against which my AC is battling! But I was wondering if the
fact that the entire system is missing has any ramifications for the cooling
of the engine.

And secondly, has anybody attempted to use any of the hot air cabin outlets
to direct cool air coming from the AC into the cabin?

Rik
Bangkok, Thailand

-----Original Message-----
From: Jim Adney [mailto:jadney@vwtype3.org] 
Sent: 19 August 2007 00:53
To: type3@vwtype3.org
Subject: RE: Rear Heat Exchanger 1972 Squareback

On 18 Aug 2007 at 9:05, Mike Perholtz wrote:

> This is great information.  I am examining the Official Service Manual
from
> Volkswagen of America and I see figure 5.1 on pg.10 of the ENGINE section.
> Part # 15 is labeled "Fresh air duct elbow".  Does air enter into this
elbow
> from the fan housing and make its way to the rear heat exchanger, or do I
> have the flow direction wrong and this elbow is in fact an exit leading
> toward the front exchangers?

Okay, I was trying to keep it simple, but I see that you're way ahead 
of me. Part of the confusion may be that this drawing shows only one 
part even when there is one per side. So there are actually 2 item 
15s, etc. The actual quantity is shown in the legend, so if you see a 
(2) there is probably one on each side.  

In addition, there are actually TWO air flow paths on each side of 
the engine.  

In all cases the cold air flow STARTS at item 27 (on each side) on 
that drawing. From there it branches into 2 paths (per side): One 
which gets heated and one which does not. The 2 paths (per side) 
rejoin just after item 15, in item 5. Here's how it works:  

The fan blows air into the elbow, item 27 (on each side.) That elbow 
carries most of the air downward into the rear heat exchanger where 
it is preheated, but some of the air branches off forward, thru items 
21, 17, 15, etc, where it does not get heated.  

The heated air continues from the rear HEs down into the lower HEs, 
where it flows forward, picking up much more heat. From there it 
flows thru # 7 and into the mixing box #5 (on each side.)  

In the mixing box there is a bellows thermostat that senses the 
temperature of the air that will be sent forward into the cabin. If 
this air is too hot, that bellows opens a valve admitting some of the 
unheated air from item 15. This may seem like an odd thing to do, but 
it allows for much more airflow into the cabin after warmup and makes 
for much better heat and defrosting.  

You can see the details of the mixing box in the cutaway view in fig 
5.2 on the next page. The mixing boxes are generally trouble free, 
but sometimes the bellows get popped if the heater has been run with 
the fresh air tubes # 17 missing.  

> Please keep in mind that the entire heating and most of the exhaust
> system was missing from my squareback when I acquired it, so I am
> mostly in the dark. 

I have most of the parts in these diagrams available in either new or 
good used condition. Most of these parts are the same for all years, 
but some changed at various times, so it sometimes takes a bit of 
work to figure out which version you need.


-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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