HEATER AND AIR CONDITIONING 1A-19
Transducer
The transducer will produce a vacuum output that is
completely adjustable by varying the input voltage which
is provided by the amplifier. An increase in the applied
voltage results in a reduced vacuum output.
Power Servo
The power servo receives a vacuum signal from the
transducer, and it is capable of assuming any position
that is called for by the sensors, amplifier, and trans-
ducer. The power servo performs the following functions:
1.
Positions the temperature mix door via the tern-
perature door link. The position of this door~"de-
termihes the portions of hot and cold air being
blended and discharged into the car.
2.
Operates the power servo vacuum valve which de-
termines the air flow paths for heating and air
conditioning.
3.
Contains a printed circuit board which controls the
blower speed. The power servo position determines
the blower speed, but the control lever switch can
override the blower program depending upon the
customer's preference.
4.
Contains the "Hi" blower delay thermistor and the
"master delay thermistor".
Outside Air Diaphragm
When there is no vacuum applied to the hose, the out-
side air door is closed under spring tension. With the
door closed, air is taken from the inside of the auto-
mobile and re-circulated. Applying vacuum to the dia-
phragm opens the door for outside air.
Mode Door Diaphragm
Located behind the duct work, the mode door diaphragm
directs the air flow out either the air conditioning outlets,
the heater floor outlet, or both the heater and air con-
ditioning outlets. This is a push-pull type diaphragm
actuated by vacuum through two hoses and controlled by
the power servo vacuum switch.
Defroster Door
The defroster door is in the defog position until vacuum
is applied to the actuator to obtain either full heat or full
de-ice position.
High Blower Delay Thermistor
The high blower delay thermistor is located on the
power servo housing under the power servo vacuum valve
and printed circuit board assemblies. The function of the
thermistor is to operate the blower at a reduced speed
when the control is in the HI FRONT position until the
residual cold air is discharged from the duct work. This
function occurs when the blower first comes "on" in cold
weather.
Vacuum Tank
During heavy acceleration, the vacuum supply from
the carburetor drops. The vacuum tank, using a^ check
valve, stores vacuum so that under these conditions
vacuum will be available for the Comfortron.
Thermal Vacuum Valve (Hot Water Vacuum Switch)
When engine coolant temperature reaches 75°F, the
valve opens and supplies vacuum to the outside air door
if the system is calling for outside air.
Master Delay Thermister
This thermistor delays the initial operation of the
blower when the system is in the heat mode. In cold
weather this allows outside ram air to flow through the
system thereby purging the cold air in the ducts gradually
until the coolant reaches about 105°F. Then, the termis-
tor passes enough current to energize the master delay
relay which powers the blower at about nine volts.
Vacuum Relay Valve
This relay valve will shut off transducer vacuum to the
power servo whenever the vacuum from the engine intake
manifold falls below the vacuum in the power servo
supply line (engine stopped or operating at low manifold
vacuum). This causes the power servo to be held in
position when the vacuum supply falls too low to maintain
servo control.
Vacuum Bleeder
A vacuum bleeder insures that the outside air door will
close (diaphragm will bleed down) after the system has
been shut down. This prevents outside air from entering
when starting the system on a cold day before the engine
coolant temperature reaches 75°F.
Sun—Ambient Sensor
The sun-ambient sensor measures the temperature of
the air entering the air intake grille in front of the wind-
shield. The sensor is exposed to sun light so that it can
lower the in-car temperature slightly when the sun
is shining.
Ambient Switch
The ambient switch operates the air conditioning com-
pressor clutch. When the outside temperature is above
40° F. the switch will be closed and the compressor will
be running. This switch is included as| part of the sun-
ambient sensor assembly, but operates independently.
Resistor Assembly
The blower resistors are located in the evaporator
housing. The printed circuit board switch in the power
servo determines which of the resistors is being used,
and as in conventional systems, the resistors control the
blower speed.
System Operation
When starting the Comfortron System in cold weather,
the following sequence of events occurs:
1.
Initially the system is inoperative. In LO FRONT
position the master delay thermistor is warming
(self-heating because current is flowing through it)
CHEVROLET CHASSIS SERVICE MANUAL
