I have a 59 GMC 100-8. The heater hoses are disconnected at the firewall. I took out the core and fan and don't see any "control valve". The control knob in the dash is a click-stop turning knob with some kind of wire-coil (resistor?) on the back side. No sign of any pull knob that might pull open a valve to turn on/off flow of water. Where did the control valve go, initially? Engine compartment, or cab? How would it have been controlled for on/off?
I'm confused!
