I have a 1972 base model camaro that came from the factory with AC. I noticed that I had a small heater core leak. So the last two days I took it upon myself to replace the heater core since winter is coming up. It was not an easy job. I did get it replaced and it seems to be leak free. However, when I took the heater box out from under the dash I noticed something. The plastic clip on the door was broken. So my vacuum pod on the back of my heater box still worked but the door would no longer move. Probably been broken for a long time. I had to WD-40 the door to get it moving properly again. I did fix it and tested with a vacuum pump to make sure all of the vacuum pods are working and that the door is working before reassembly. I was wondering what the A/C Heater Diverter door does exactly. When I had the heater box out I was looking at it. Looking at it it looked like it had three positions. Halfway open/closed which is the position it was stuck in when I pulled it out since the plastic clip was broken. The other two positions are operated by the vacuum pod on the back. They seem to direct air to the heater core and toward the defrost or bypass the heater core and direct air out the vents. Can anyone confirm what positions this door is supposed to work on the heater controls and its exact function?