I'm curious about the vents on the passenger side cowl. I believe it was 1955 when GMC added a vent door on the inside that could be opened or closed for cool air ventilation. However on my '51 GMC and my buddy's '52, there is just an access panel on the inside that screws on (6 screws). Once you take that access panel off you can see the vents on the outer cowl. But they don't seem to serve any purpose. Does anyone know why they are there?
GMC offered 2 heaters as shown below from the '53 GMC Master Parts Book. The one on the top was also known as the "fresh air heater". You remove the panel with 6 screws and bolt the right side of the heater into the hole. The one on the bottom is known as the "recirculating heater".
Would you happen to have any links to promotional literature on these heaters? I'm curious how they convert cold air into hot air? Not to mention how they would work during a traffic jam in January? I could see them being marketed as a cooling unit to compliment the standard heater to be used in the heat of the summer, since GMC omitted the flip out front windshield. However the defroster tubes don't have provisions (Y) for the tubes coming from the conventional heater. You mentioned that they were available in the '53 parts book. As I'm sure you know, the louvers were there from the start of this body style in '47. Before I was puzzled, now I'm confused. ???
I have no promotional lit. Hot engine coolant (water/antifreeze mix) is pushed into a 3/4" diameter hose by the engine's water pump. The other end of the hose is connected to a small "core" in the heater, similar to the radiator in front of the engine. Coolant is then returned to the engine through a 5/8" hose. The heater core warms up because of the high temp coolant passing through it. An electric fan moves cabin air (or outside air through the previously discussed removed "panel with 6 screws") over the core, heating the air, which is then returned to warm your toes and/or defrost the windshield, depending on the setting of the defrost lever on the heater case. My '52 GMC came to me in 2013 with the pieces that bolt up to the defrost vent holes in the dash near the bottom on the windshield. I'm assuming these are the "(Y) for the tubes coming from the conventional heater." I live in the country, so no traffic jams. I'm in south central Texas, so probably not as cold or damp as in BC.
I'm amazed at the "theory of function" for these accessories. They seem counterproductive at best. The conventional heater had been around for some time by the time these trucks came on the market, and haven't changed mush since then. But someone at GM sitting at a drafting table decided that "cold" air would produce better and faster heat than hot air????? Am I missing something here?
Not better nor faster. Fresher. Remember, the majority of adults in 1951 smoked. Opening the heater input to outside air and cracking open the wing window would help to clear the smoke out of the cab.
