Cadillac 1967 VVI Data Book page 152

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After initial settings are made, it is recommended that the
system be left "ON" at all times for maximum comfort. The
air conditioner-heater system will operate automatically when-
ever the car is started; it will start almost immediately in
warm weather, but heater operation in cold weather will be
delayed until heat is available from the engine coolant.
Additional settings
Five additional settings of the control lever are provided for
use in those instances when extreme weather conditions call
for extra or reduced volumes of heated or cooled air, outside
air or for air to be directed to the windshield.
The "LO" setting causes the system to operate as in the
"AUTO" setting but at a fixed low blower speed, reducing the
volume of air.
The "HI" setting causes the system to operate as in the
"AUTO" setting but at maximum blower speed, resulting in
quicker cool-down in summer and warm-up in winter. Also,
it allows the air conditioner to operate on 80% recirculated
air for maximum cooling efficiency.
To achieve quicker cool-down when the car has been
parked in the hot sun, the end outlets should be positioned so
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