Electrical Components; Functional Test - Pontiac FIREBIRD 1972 Service Manual

1 B-42
1972 PONTIAC SERVICE MANUAL
upon the system by varying weather conditions. High
range will give most uniform comfort throughout the car,
especially with rear seat passengers.
ELECTRICAL COMPONENTS
In addition to vacuum functions, the programmer also
performs electrical functions. A small current passing
through the sensors and control panel variable resistor
creates an electrical signal which controls the program-
mer. The voltage signal which the programmer receives is
dependent on the resistance offered by sensors. (Sensor
resistance is high at low temperatures and low at high
temperatures). The programmer takes this voltage signal,
amplifies it and then passes it through a small motor,
which drives a wheel. The surface of the wheel has several
switches on it which direct current to various portions of
the system. In addition, the wheel is linked to the tempera-
ture door, the position of which determines the outlet
temperature of the system.
The programmer controls blower speed by directing cur-
rent through one or more of several resistors in a resistor
block located on the evaporator case. As the number of
resistors through which the current must pass increases,
voltage supplied to blower motor decreases, thereby de-
creasing its speed.
The limit switch and location switch, also on the surface
of programmer wheel, have the following functions. The
limit switch stops the movement of the motor and wheel
when it reaches its extreme point of travel in either direc-
tion. The location switch allows current to drive program-
mer wheel (and temperature door) to a midway position
after system is turned off. This eliminates extreme hot or
extreme cold blasts of air when the system is first started.
The bi-level boost switch has the special function of speed-
ing up the blower motor when the diverter doors move
into bi-level mode. The switch is mechanically operated by
the movement of the diverter doors. When the switch is
closed, a path through the resistor block which provides
a relatively high blower speed is provided. This is done
because all the distribution ducts are used in the bi-level
mode which requires a greater quantity of air movement.
The remainder of the electrical components such as the hi
blower relay, compressor clutch coil, line and fuse block
fuses and ambient switch all function the same and are
located in the same positions as corresponding compo-
nents of the Custom Air Conditioning (A/C) system.
switch. The switch is rotated by a wheel which is in turn
driven by the programmer motor. Vacuum from this
switch controls the water control valve, diverter doors,
defroster door and the air inlet door. It is important to
note that some of this vacuum control is also initiated by
the control head vacuum valve.
FUNCTIONAL TEST
This test must be performed on complete car with engine
operating, coolant warm, hood closed and approximately
75°F. ambient temperature.
1. Move selector lever to OFF, set blower switch to HI
range and move temperature lever to full WARM (all
the way up).
A. No air flow from any outlets.
2. Move selector lever to NORMAL. (Each lever posi-
tion has a detent to lock the lever in place.)
A. Blower comes on low speed and progresses to
high speed.
B. Hot air comes chiefly from heater outlet with
some air from defroster nozzles. None from A/C
outlets.
3. Move temperature lever to full cold (all the way
down).
A. Air will come out A/C and heater outlets at the
same time and then from A/C outlets only. Fi-
nally, blower noise level will increase with cold air
coming from A/C outlets only.
B. Blower speed goes from "Hi-Lo-Hi" with an in-
crease in blower speed in bi-level (warm air out
heater and cool air out A/C outlets).
4.
Move temperature lever slowly up until air comes out
A/C and heater outlets at the same time, then move
selector lever to INSIDE.
A. Blower air noise level will increase.
5. Move temperature lever back to full cold and put
selector lever in the DEFOG position.
A. Cold air comes chiefly from defroster nozzles,
with some air from heater outlet.
6. Move selector lever to DEFROST.
AIR FLOW COMPONENTS
Air flow in the ATC system is the same as in the Custom
A/C system. Vacuum functions are initiated in a slightly
different manner, however. The programmer directs
vacuum to various diaphragms in the system via a vacuum
A. Air continues to come chiefly from defroster noz-
zle with some air from heater outlet; but tempera-
ture changes from cold to hot.
B. Blower goes to high speed.