Nissan Repair: Heat, 2006 nissan frontier, heater hoses

Question
I have a 2006 Nissan frontier 4.0L. The heat comes and goes intermittently.The fan and vent controls all work fine, just the air temp changes back and forth. My temp gauge seems normal.

Answer
Larry,

Feel the heater hoses.  If both are hot then it is a blend door under the dash that is moving back and forth.  Sounds like the vacuum canister is not working properly.  That feeds constant vacuum to the controls.  If the check valve fails vacuum drops off every time the throttle is depressed.