Vacuum System Diagnosis; R/V And G-Van; Evacuating And Charging Procedures; Discharging, Evacuating, Adding Oil And Charging Procedures - GMC G Service Manual

1B-24 AIR CONDITIONING

VACUUM SYSTEM DIAGNOSIS

R/V AND G-VAN

Start the engine and allow it to idle. Move the selector
lever to each position and refer to the vacuum diagrams
and operational charts for airflow, air door functioning and
vacuum circuits. If airflow is not out of the proper outlet at
each selector lever position do the following:
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Inspect
1. The hose connections at the vacuum actuators, con­
trol head valve and vacuum tank.
2. The vacuum source circuit:
• Install a vacuum tee and gage (with restrictor) at
the vacuum tank outlet. Idle the engine and
read the vacuum (a normal vacuum is equiva­
lent to manifold vacuum) at all selector lever
positions.
• Vacuum less than normal at all positions.
Remove the tee and connect the vacuum gage
line to the tank— read the vacuum. If still low,
the problem lies in the feed circuit, the feed cir­
cuit to the tank or in the tank itself. If vacuum is
now normal, the problem lies downstream.
• Vacuum less than normal at some positions.
If vacuum was low at one or several of the
selector lever positions, a leak is indicated in
these circuits.

EVACUATING AND CHARGING PROCEDURES

Before opening any refrigerant hose or component, read
the information provided in:
• Refrigerant-12 Operating Characteristics.
• Discharging, Evacuating, Adding Oil and Charging
Procedures.
Remove sealing caps from subassemblies before mak­
ing connections for final assembly. Use a small amount of
clean 525 viscosity refrigerant oil on all tube and hose
joints.
Use new seal (O-ring) dipped in the clean 525 viscosity
refrigerant oil when assembling joints. The oil will aid in
assembly and help provide a leak-proof joint.
When tightening joints, use a second wrench to hold the
stationary part of the connection.
• Vacuum normal at all positions.
If vacuum was normal and even at all positions,
the malfunction may be caused by improperly
connected or plugged lines or a malfunctioning
vacuum valve or valves.
3. Specific vacuum circuit:
• Place the selector lever in the malfunctioning
position and check for vacuum at the pertinent
vacuum actuators.
• If vacuum exists at the actuator but the door
does not move, the actuator is malfunctioning or
the door is jammed.
• If low or no vacuum exists at the actuator, deter­
mine whether the cause is the vacuum harness
or the vacuum valve.
• Check the vacuum harness first.
4. Vacuum harness circuit:
• Disconnect the vacuum harness at the control
head.
• The black line should show engine vacuum; if
not, trace back through connector to vacuum
tank.
• To check any individual circuit, place the selec­
tor lever at the involved circuit position and
check for vacuum presence.
Tighten all tubing connections to specification (figure
10). Insufficient or excessive torque can cause loose joints
or deformed joint parts. Either condition can cause leakage.
DISCHARGING, EVACUATING,
ADDING OIL AND CHARGING
PROCEDURES
Discharge, evacuate and charge using J 23500-01 air
conditioning service Charging Station or the J 23575-01
Manifold Gage Set, and 0.397 kg. (14 oz.) disposable cans
of Refrigerant-12 (figures 24 and 25).