The 1964 Riviera has a 4-speed fan (high, medium, low, and
low-low). The heater/defroster only uses the 3 lowest speeds. That is,
the high setting on the heater fan switch is the same fan speed as the
medium setting on the A/C fan switch.
I figure that if there's one time I want full-on air, it's when I
want to defrost my windshield. Therefore, I rewired the connector to
the heater blower switch. You have to disassemble the blower switch
connector to do this, but you can do all of this just by pulling the
A/C controls out of the console. Insert a small screwdriver in the
front of the connector to depress the locking tang, then pull the wire
out the back. I tapped a lead off of the high-speed connector (gray
wire) from the A/C blower switch and put that in the heater high
position. I also moved the low wire (light blue) to the low-low
position, and the medium wire (orange) to the low position. I
disconnected and taped up the now unused low-low wire (yellow). I
essentially moved every switch position up one blower speed. See Fig.
11-57 in the shop manual.