high limit switch

We have an old Whitfield Advantage II and it was suggested we check the high limit switch to see if that is the problem of our pellets to stop feeding but we can't find the switch. Anyone know where it is and also the intake air hose we can't seem to find one of those either. Checked the auger motor and it seems to be okay. Stove works for abot 45 minutes then quites feeding, if we tap on the auger it will feed for about 1 minute then quit again. Shut the stove down cleaned everything started it up again and same thing happened. New exhaust pipe everything has been cleaned. What next?

the first two photos on this post is the vacuum switch and hose

http://www.hearth.com/econtent/index.php/forums/viewthread/13499/