If this is the heater that you have, then it's the optional
Deluxe Fresh air Heater from GM:
http://www.pbase.com/dennygraham/image/141790251 If the tube on the left is missing then the thermostatic control
is shot, they can't be repaired either. Finding a donor is the
only repair for the Ranco valve. The only regulation that you
have, as you have already discovered is to turn the blower
motor on and off. With out the fan blowing across the core you
won't get a lot of heat. On the low speed the fan switch
dropping resistor will get super hot so watch it, don't burn
your fingers feeling around behind it.
Doesn't sound like it's a recirculating heater because it has
a round heater core:
http://www.pbase.com/dennygraham/image/149025181If it's something along the lines of this then it's an aftermarket heater
as Charlie pointed out from an auto parts store that someone installed:
http://www.pbase.com/dennygraham/image/149025155 Denny Graham
Sandwich, IL
