air conditioner/heater woes

[stevemash]

hi all,
our 96 ssei has sat for a while. now, with the air recently serviced, it blows hot air when turned on. my air tek guy, a buddy, says the heater door must be "open" and is not closing when the unit calls for air.
the dash looks intimidating!!! does anyone know where this heater door is located at? i'd hate to dig in the wrong spot, so to speak.
thanks
steve