Heater Box/Heater Blower Resistor Block/Vac Schematic

88 Cherokee, 4.0
Passenger side, passenger compartment, under the dash is what appears to be an air handling box with a big vacuum operated door on it. Can anyone tell me (or know where I can get aftermarket info) as to what controls that vacuum motor? Is it exclusive for use by the air conditioning system? It seems as though whatever heating function I choose, I can't get it to operate...(Hotter air/higher cabin temperature wouldn't hurt either, it's why I wonder about that door being inoperable always allowing outside air into the system...)
The next question is, "Does anyone know the value of the resistor on the Heater Blower Resistor Block?" The toasted resistor would appear to be all that's wrong with that block, but it's so discolored, I can't read the color bands on it. (Again, an aftermarket source for this part would be appreciated too as my local auto parts places tell me it's a "Dealer Item Only"...)
And as a I asked in another response, any information as to where I can get an aftermarket vacuum schematic (other than what the Hayne's manual offers about emission control) that addresses four wheel drive function/heating system, etc. would be appreciated.

Stephen

There should be a football looking tank inside the passenger front bumper this controls the register?(where the air goes floor,vents,defrost.) On the back of control unit should be some vacuum lines plugging in to the control unit, make sure they are pressed in firmly. The door only opens on max a/c w/ mine I think. Also while you have control unit out make sure the plug in to the main wiring harness is good had problems w/ mine recently. For parts try going to a Junkard. Good Luck!