71 Heater

A couple of months ago I posted a question that I only had hot air blowing out of the passenger side of the heater and defroster and cool air blowing from the drivers side. Several people responded, but were pretty stumped. Bu we all agreed that the heater core was probably blocked. Well that wasn't it. After tearing the whole thing apart I found that the vinyl that makes-up the seal on the metal vent door had fallen away and was lying on the drivers side of the heater core. Of course I replaced the heater core and all of the seals while I was at it and now it works perfectly. Thanks for all the inputs. Hope this helps someone else out.
Kevin