I've been trying to locate the heater door to ensure it's closing and I just couldn't find it. Last night I REALLY went looking. I pulled out the passenger side duct work and followed the cabel to the top of the blower box on the passenger side fire wall. Still couldn't see anything so I pulled the glove box. On top of the blower box was a vacuum switch that gets pressed when the cold/hot lever is moved all the way to cold.. Mine wasn't reaching.. I adjusted the cable to reach and depress this switch. I also found one of the tiny vaccuum hose connected to this switch was wrapped over one of the mounting brackets, kinked and abviously not working. I followed the two tinny hoses through the firewall.. One went to the main vacuum line and the other to a vacumm canister in the heater line. Pretty much where I was thinking about putting the manual petcocks to shutoff the water flow to the heater coils. I warmed up the car and got cold air when on cold.. warm air as soon as the switch was released. I still can't see the door but I'm guessing the adjustment completly closed the door and now also shuts off the supply of hot water to the heater coil. It was a good night last night.. I felt productive enough to tackle my passenger side mirror.. not as lucky there..

Just wanted to share what I found! :cheers: