Posted by Mark [172.68.142.206] on Tuesday, January 07, 2020 at 14:18:38 :
In Reply to: Re: Hole in back of heater box, '71 Power Wagon posted by Kaegi [108.162.246.200] on Tuesday, January 07, 2020 at 02:09:23 :
I have been thinking about the effects of leaving the hole uncovered and agree that it might not make much of a difference particularly if the box is tight up against the firewall.
However, if there is not a tight fit then that means cabin air will be pulled in from the rear of the box and thus limit the effectiveness of either the external air damper or cabin air door.
On the other hand, I wonder what happens if the external air damper is closed, and the cabin air door is closed and the heater blower motor is turned on. That would create a suction effect if the blower motor tries to pull air through the heater core.