GMC chevrolet camaro 2000 Service Manual page 247

1 "'.150 HVAC Systems - Manual
The engine vacuum regulates all of the actuators (3, 10,
12 and 13) (except the temperature valve) in the heater
and air conditioning (A/C) evaporator module. The
vacuum is drawn from the vacuum tank (1 ). The tank is
mounted to the right side body rail.
A vacuum selector valve routes the vacuum to
spring-loaded vacuum actuators (3, 10, 12 and 13) on
the heater and A/C evaporator module.
During conditions of low engine manifold vacuum, a
check valve in the vacuum source hose prevents
vacuum in the vacuum tank from bleeding back to the
vacuum's source.
The mode control regulates the vacuum selector
valve. At each mode control position, the valve
performs the following actions:
" Directs vacuum to the specific hoses in order to
overcome the force of the spring within the
actuators.
O
Vents the hoses to normal air pressure. This
action allows the spring to expand. The expansion
results in the proper positioning of the valves
(doors) for the selected operating mode.
The vacuum (bi-level) (10) and vent valves have
two-position vacuum actuators. When vacuum
i.s directed to either actuator's vacuum chamber, the
vacuum pulls in a flexible diaphragm. The diaphragm
forms one wall of the chamber. This action draws
a movable shaft attached to the diaphragm. The shaft
is linked to the corresponding valve. The shaft
operates the valve when the vacuum is applied.
An external spring moves the shaft back to its original
position when the vacuum chamber is vented to
normal air pressure. The shaft, .in turn, returns the
valve to its original position.
The heater and defrost valve (13) uses a three-position
vacuum actuator. A three-position vacuum actuator
has a diaphragm with a spring on both sides. At rest
(no vacuum applied) the diaphragm is in a
mid-position. This allows for a blend mode. Apply
vacuum to either end of the diaphragm in order
to move the heater and defrost valve to either stop.
This action directs airflow to either the defroster outlets
or the floor outlets.
When air is directed to the floor outlets, as in the
HEATER setting, a small amount of air still bleeds
through the defroster outlets. This. action helps
eliminate the refogging of the windshield.
HVAC
HVAC Blower Controls .Circuit Description
LOW-M2 Positions (
When the ignition switch is in the RUN position,
voltage is applied through the HVAC Fuse 6 (20A),
the ignition 3 voltage circuit of the HV AC control, to the
HVAC control (selector switch). When the selector
switch is switched to any position, except OFF, voltage
is supplied to the blower switch through the A/C
request signal circuit.
When the blower switch is in position 1 (low), voltage
is applied to the blower switch, the blower resistor,
the blower motor relay and the blower motor.
When voltage is applied to the blower motor, the
motor runs at lo.w speed.
When the blower switch is switched to position 2 (Mi)
or 3 (M2), the blower control system works as
described above except for the speed of the blower
motor. The blower motor has several resistors
that voltage flows through depending which position
the blower switch is in. In position 1 (low), voltage
passes through 4 resistors. In position 2 (M1 ), voltage
passes 3 resistors and in position 3 (M2) voltage
passes through 2 resistors. As the resistance
is decreased the blower runs at a faster speed.
HIGH Position
When the blower switch is moved to position 4 (high),
voltage is applied through the HVAC control (selector
switch) to the blower motor relay. The relay
energizes, turning on the blower motor. This causes (
the motor to run at its fastest speed due to the fact that
there is no resistor in the voltage path to the
blower motor.