Pontiac FIREBIRD 1972 Service Manual page 210

AUTOMATIC TEMPERATURE CONTROL 1B-23
(A) WlTH ENGINE RUNNING A T OPERATING TEMPERATURE,
(0) NORMAL
,
BLOWER RANGE SWITCH S E T TO HI, TEMPERATURE CONTROL S E T TO75"AND SYSTEM STABILIZED,
(C) USING A 12 VOLT T E S T LAMP O R A VOLTMETER, WlTH ONE PROBE TO GROUND
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INSERT OTHER PROBE INTO BLACK WITH SINGLE RED STRIPE WIRE A T 81-LEVEL BOOST SWITCH
1
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T E S T LIGHT LIGHTS
INSERT PROBE
W O
DARK BLUE Wl R E A T 81-LEVEL BOOST SWITCH.
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T E S T LIGHT DOES NOT LIGHT
CHECK WIRING BETWEEN PROGRAMMER AND SWITCH.
TEST M
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T E S T LIGHT LIGHTS
- -
CHECK WIRING BEWEEN SWITCH AND PROGRAMMER
REPLACE DIAPHRAGM
REPLACE 81-LEVEL BOOST SWITCH.
(A) WlTH ENGINE RUNNING AT OPERATING TEMPERATURE,
6 ) INSIDE
,
BLOWER RANGE SWITCH S E T TO HI, TEMPERATURE CONTROL S E T TO MAXIMUM HEAT
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NO VACUUM
CHECK FOR VACUUM AT WRT 7 0 F CONTROL PANEL VACUUM VALVE.
,
REMOVE ORANGE HOSE FROM SINGLE DIAPHRAGM AT AIR INLET DOOR. HOSE SHOULD HAVE VACUUM.
Fig. 18-20 ATC Diagnosis Guide
GENERAL DESCRIPTION
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Automatic Temperature Control (ATC), an expanded
version of the Custom Air Conditioning system(A/C),
provides automatically controlled interior temperatures.
With this system the driver can set desired interior com-
fort level with a lever (or dial) located on the ATC control
panel. The Automatic Temperature Control system will
then maintain the set comfort level regardless of weather
and requires little or no change in setting to compensate
for changes due to outside weather conditions.
VACUUM
CHECK ORANGE HOSE FOR LEAK OR RESTRICTION.
Automatic control of temperature is beneficial in both
summer and winter. In hot weather, it will cool the car
rapidly to a pre-set comfort level and then modulate cool-
ing to whatever degree is required to maintain constant
comfort. In mild weather, the interior of the vehicle re-
mains comfortable without having to reset controls. In
cold weather, the system will heat the car quickly to a
desired temperature, stabilize and then maintain the pre-
set comfort level. This control, however, will not compen-
sate for variations in comfort level desired by individual
passengers.
NO VACUUM
G~KFXKTROL
PANEL VACUUM VALVE.
The system, when in operation, will remove excess mois-
ture from the air when the compressor is engaged and in
operation. This removal of excess moisture from the air
increases passenger comfort, particularly while traveling
in humid weather, and limits window fogging and interior
condensation.
The Automatic Temperature Control system makes use of
two temperature-sensing devices, called thermistors, for
its operation. One, near the glove box on the instrument
panel, senses vehicle interior temperature. Another,
located in air passage from the cowl vent opening, senses
temperature of incoming air. These sensors are wired in
series with a temperature potentiometer (variable resistor)
on the control panel. As temperature in the area of the
sensors varies, the total series resistance also changes and
a variable input signal is supplied to a D.C. amplifier. This
variable signal through the amplifier determines the
amount of heating or cooling by changing the position of
a unit called the programmer, which controls the tempera-
ture door in the heater case, the rotary vacuum valves and
the blower, which in turn regulate the air temperature, air
quantity (blower speed) and air distribution patterns
(heating and/or air conditioning). The remainder of the
system is basically the same as the Custom Air Condition-
ing 'system.
SENSORS (THERMISTORS)
A sensor (semi-conductor thermistor) is extremely sensi-