I need some help with a Blend Door problem. The heat/air coming thru the vents after the truck warms-up, goes from hot to cool, then to hot, then to cool, etc...then it seems to just stay hot.. So, I thought that my BLEND DOOR was broken, as a lot of you have said on this forum, So, I ordered a new door from Rock Auto. I made the cut-out of the plenum
box, as showen on www.heatertreater.net/F150%20video.html. BUt, after making the cut-out, I discovered that the BLEND DOOR is NOT broken.... so I then removed the black plastic from the center hump, and looked at the blend door actuator as I moved the heat control from cold to hot, it seemed to move alright. Close...open...close...open... THEN, after the truck had ran for about ten minutes, the door started to open and close by itself, VERY ERATICLY. Does thgis mean that my actuator is BAD....???? Any HELP would be APPRECIATED....

P.S. When the Heat/Panel/Air switch is in the OFF position....the door stays closed......