A real close up of a fresh air heater core and control valve! Most were not seen in combination in a GM truck unless repairs were needed.
Thus, this may be of interest to owners doing restoration. This is how GM heater designers were able to incorporate an in-dash control cable to the water control valve. They created a water control valve that attached to a right angle bracket on the top of the core. This core and the delicate valve are protected by the sheet metal heater box.
Once heated water from the engine enters the valve (to be flow adjusted by the dash control cable) it goes to the thick square heater core.
The heater fan forces air through the core fins. Here ,air is immediately warmed, depending on the speed of the water flow. The slower this flow, the more hot water can heat passing air from the fan.