The 1952 "fresh air" system did not look like the 1953 "fresh air" system.
The 1947-1952 "deluxe" GM heater had no interior door for recirculating interior air (part number 186904 for all those years).
In 1947-48, the "deluxe" heater was called (in Chevrolet Accessory Manuals and in Accessories Lists) the "Fresh Air Heater"; and, in 1949-1952, the heater was called an "Air Flow Heater". The heaters appear to have been the same over all those years (47-52). On these heaters, there was a cable-controlled defroster "flap"/diverter.
The name-tags (metal/aluminum plates with attachment tabs on them) might have been the same on all 47-52 Chevrolet truck heaters (recirculating and "deluxe"). However, in the very poor quality pictures in the 1950 Accessories Installation Manual, the image on the Recirculating Heater's name-tag plate appears to be slightly different from the Air Flow heater's plate.
In 1953, the "deluxe" heater had an interior door (with a cable control) and was part number 986709. The defroster "flap"/diverter was a hand-controlled lever (similar to the one used on the more common recirculating heater). 1953 documentation also called this heater an Air Flow heater.
The 1954/55-st "deluxe" heater also had the interior door (as was used in 1953), and it was called an Air Flow heater, but the part number changed to 986895.
The 1953 and 1954 Accessories Installation Manuals use the same installation illustrations/directions for the cable-controlled interior door on the "deluxe" heater (including showing in the 1954 Accessories Installation Manual the 1953 knob on the cable-controller for the interior door).
My guess is that the 1953 heater had a different part number than the 1954/55 heater due to the change in the style of the cable controller knob.
Supposedly, the 53-55st Air Flow heater used
the same decal, which was supposedly different from the
earlier, metal plate. And, this 53-55st Air Flow heater decal was different from the 53-55st
Reciculating Heater decal.
Is that confusing enough?
Since the heaters were either dealer-installed (or owner-installed) and obtained through a dealer, an earlier Air Flow heater (without the internal door) might have been installed on a 1953 or later truck (if the dealer had the older "deluxe" heater in stock).
