have a 1999 blazer lt with atc and the blend door will constantly go from full hot to full cold and never stay at a set temperature,dosent matter if it is auto or not is a/c control head bad or is it actuator motor?

 

ttt

I have an actuator on the blend door that turns every 15 seconds or so.

 

it maybe the temp sender at the drivers door head liner . the waffle looking thing at door.