2001 F-150 Lariat Crew Cab My blend door is working eratically...all by itself...the door is not broken....(I have the manual controls...) I don't see any vacuum hose at the firewall behind the battery, only a power connector... The actuator is working also.... When AC is on it also does the same thing...hot to cold to hot....DOES ANYONE have any ideas.. I NEED HELP on this please.. Could this be a problem with the TEMP control...??

PS... I found the vac line directly against the battery (I didn't see it).. All the connections seem all OK...hoses a little old, buy seem AOK..
ALSO, when I start the truck, in PANEL mode, (cold) the temp control moves the Blend Door, OPEN...CLOSE...OPEN...CLOSE...no problem,
But, after warming up, the door moves all by itself..........