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One point of interest; this Valve came on all trucks of the time with the Harrison Deluxe Heater, and it did not come on the ones with the Fresh Air (round core) Heater right? If that is correct, what did the Fresh Air Heater folks do for thermostatic control?
Fresh Air and Air Flow were the names used for the heat-control-valve "deluxe" heaters between 47-55. From 53-55 these heaters were truly "Fresh Air" heaters, in that they had a control cable to let fresh outside air pass through the heater core (defrost was controlled by a lever similar to the lever on a Recirculating Heater). From 47-52, the control cable controlled defrost vs downward/floor heat.
As Mike posted, the 47-55 recirculating heaters did not have a heat control valve.
