Cadillac 1967 VVI Data Book page 173

Rear system controls
The controls for the rear system, consisting of an on-6ff switch
and a temperature dial, are located underneath a hinged cover
in the right rear armrest. The rear system may be turned on
and off with the switch, and temperature may be controlled
by the temperature dial. To reduce or increase the temperature,
rotate the temperature dial to the interior temperature desired.
Since the system is completely automatic, it may be set at a
comfortable temperature setting and left on with virtually no
further adjustments required due to outside weather con-
ditions. In cold weather the heater will automatically turn on
when engine water is warm enough. When outside tempera-
tures are high, the system will automatically provide air
conditioning.
In cool weather, warm air is delivered from the trunk unit
through ducts leading into the rear doors, then into the rear
passenger compartment through grilles located beneath the
rear door armrests.
In warm weather, cooled, dehumidified air is delivered
through ducts in the roof and out of overhead grilles into the
rear passenger compartment. The outlet grilles are equipped
with a number of small openings for providing diffused cooled
air. Each outlet is equipped with a hinged door that may be
opened to direct air toward the rear passengers.
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