Paul,

 

Usually a heat valve is in the shape of a T  where the heated air comes in the bottom and the valve directs it either left or right.  I.E. Either out the front into the lower cowl where a tube should carry it to an area that is in the lower cowl exit stream or through the firewall into the cabin.  Of course in a partial position some air is sent both ways.  The usual problem is not connecting the input air to the bottom of the T.

 

Here are some pix of my 320  heat muff supply air entry opening in front of cyl #2 and a summer cover plate with a small hole to reduce the air that is going to bypass heating the cabin but enough to not let the aluminum muff overheat.  I just had to loosen three screws to slip the plate on or off.

 

 

Grayhawk

 

Someone mentioned the Legacy bleed hole for the heat muff is the largest in the upper deck.  I checked and it surprised me that on my Legacy the hole is plumbed to the heat muff 100% of the time and dumps overboard when heat is OFF.   IF the heat control is opened in the cockpit, the valve on the inside of the firewall opens up and it appears the overboard and cockpit exits are in parallel.  In other words, it dumps overboard and into the cabin.

So, in warm weather, why wouldn't we want that hole closed off?    Does the heat muff need that airflow?  I used heat maybe 3 times last year.  What is the effect of plumbing the valve so that it closes off the exit from the upper deck?  That way you get heat when needed but no losses when not needed.  The muff would not get airflow in this case.   I would not do that unless I had some idea of the effects but it seems a huge cooling loss 100% of the time when it really isn't needed.

Paul
Legacy
Calgary
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