Long, long ago when I was small, my parents bought new the '54 Chevy listed below. Back then, heaters were optional. They had the OE type heater installed by the dealer. Unlike later US cars, the heater supposedly offered a choice of outside or inside (recirculated) air intake. However, the outside air setting was useless in winter, because it provided meager output of warm air, and simultaneously lots of cold air through another outlet. So, they always used the recirculate setting, which required using the fan to get any air output.
At least a decade later, as a teenager, I got curious and investigated. It turned out the dealer mechanic had misadjusted one of the control cables. After I adjusted it, the heater functioned much better with outside air intake. By then, the old Chevrolet was only a backup for their newer primary car.