GMC Chevrolet Camaro 1998 Service Manual page 145

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HVAC
Mode Control Vacuum Valve Positions
1 OFF
2 MAXA/C
3 NORMALA/C
4 Bl-LEVEL A/C
5 VENT
6
HEATER
7
HEATER/DEFROST BLEND
8 DEFROSTER
A vacuum operates most of the air distribution system.
Electrical power operates the blower motor.
The engine vacuum is routed through the
following areas:
• The vacuum check valve
• The control vacuum selector
• The vacuum tank
The vacuum check valve prevents vacuum loss.
Heavy acceleration or steep uphill traveling may cause
vacuum loss.
Vacuum applied to a vacuum actuator moves the air
door to the air door's correct position.
Preliminary Inspection
1 . Inspect the vacuum lines at the engine and
vacuum check valve for a proper connection.
2. Disconnect the vacuum line that leads to the
engine at the vacuum check valve.
HVAC System - Manual 1-35
3. Start the engine.
4. Inspect for vacuum presence. If no vacuum is
present, repair as required.
5. Disconnect the vacuum line that leads to the
vacuum tank at the vacuum check valve.
6. Use a hand vacuum pump in order to apply
vacuum to the vacuum line that leads to the
vacuum tank. If the vacuum does not hold, replace
the vacuum line and/or the vacuum tank.
7. Disconnect the vacuum line that leads to the
control at the vacuum check valve.
8. Apply vacuum to the check valve port. If the
vacuum does not hold, replace the vacuum
check valve.
9. Quickly rotate the temperature control from full
COLD to full HOT several times.
10. Listen for the temperature valve to seat in both
positions.
If the sound indicates that the temperature valve
is not fully seating or opening, inspect the
temperature control cable for proper operation. If
the problem persists, ensure that the temperature
valve door operates freely with the blower off.
11. Ensure that the vacuum line seals are positioned
correctly at the vacuum line multi-connector that is
located above the right-hand sound
insulator panel.
12. Perform the diagnosis.
Diagnostic Aid
Checks Action
Apply vacuum to the red vacuum line. Air flow is diverted to the instrument panel outlets only.
Apply vacuum to the yellow Air flow is diverted to the side window defogger and floor outlets.
vacuum line.
Apply vacuum to the purple
Air flow is diverted to the side window defogger, floor and instrument panel outlets.
vacuum line.
Apply vacuum to the green
Air flow is diverted to the windshield and side window defogger outlets.
vacuum line.
Apply vacuum to the orange Air flow is diverted to the blower motor assembly air noise increase.
vacuum line.
Apply vacuum to no vacuum lines.
Air flow is diverted to all outlets except the instrument panel.
Improper Air Delivery Diagnosis
Step Action Value(s) Yes No
1. Perform the preliminary inspection.
2. Set the mode selector valve in the OFF position.
3. Disconnect the vacuum line at the check valve.
1
4. Use a hand vacuum pump in order to apply vacuum
-
to the vacuum line that leads to the mode
selector v.alve.
Does the vacuum hold?
Go to Step 3 Go to Step 2
1. Inspect the black vacuum line that leads to the mode
selector valve.
2
2. Replace the mode selector valve if the line is
- -
connected and working properly.
Is the replacement complete?
System OK