I have an 86 K5. Last winter the heat just stopped working. Spring was coming so I just didn't mess with it. Today I started dinking around and behind the glovebox I found the wire from the heat/cold slider had slid off the flapper lever. I fixed that and the heat is working now. My question is next to the heat flapper arm there is another flapper type arm connected to the same type of cable. For the life of me I can't figure out what it is for. Maybe something to do with the AC (the underhood ac stuff was taken out). Also, are the defroster and the dash vents supposed to use the same duct? I don't get any flow out of the defroster unless the dash vents are closed. TY in advance.