I have noticed that the operators manual for 1959 Chevrolet trucks don't seem to address a heater, if so equipped.
I've looked around a little on the internet for possible GM literature concerning heaters, but havn't found anything.
Did GM produce literature concerning heater operation? It would seem that with the detail early operator's manuals go into concerning other functions and procedures, they would have written up something detailing heater operation.
Granted, heaters are pretty easy to figure out..but for a complete glovebox, one would want all the instructions...
