i have a 2003 kw 900l does anyone have any ideal why air will blow good out of heater vent but not much at all out of defrost or dash vents.i have replaced fan and resistor with no luck.
You must look behind the heater temp control panel small lines lead to box with flap inside,1st find out if air is geting to flap ck. if flap will move by hand.one of many is air supply line ck. for air.