GMC 4000 Series Service Manual page 91

Sec. 1
Page 84________________
AIR CONDITIONING
EVAPORATOR
4. The system can now be evacuated.
EVACUATING COMPLETE SYSTEM
1. Turn hand shut-off valve on low pressure
gauge of gauge set to the full clockwise (closed)
position.
2. Slowly turn valve on high pressure gauge
counterclockwise from the full clockwise position,
letting any pressure build-up escape completely.
Close high pressure valve.
3. Check oil level in vacuum pump ( J-5428-03)
and add Frigidaire-150 viscosity oil or equivalent,
if necessary, to bring to proper level. Make sure
dust cap on discharge side of vacuum pump has
been removed.
4. Start the vacuum pump and slowly open the
low and high pressure sides of the manifold gauge
set to avoid forcing oil out of the refrigeration
system and the pump. Pressure is now being reduc­
ed on both sides of the refrigeration system .
NOTE: If oil is blown from the vacuum pump,
it should be refilled to the proper level with Frig­
idaire-150 viscosity oil or equivalent.
G M C S E R V I C E M A N U A L
SUCTION THROTTLING VALVE
r
: I V
FROM RECEIVER-DEHYDRATOR
Figure 12— H ook-U p of G auges and C harging Equipment
C OM PRESSO R
/
______
LO HI
DRUM ^ J
" 0 7
REFRIGERANT-12
5. Observe low pressure gauge and operate
vacuum pump until gauge shows 26-28" vacuum.
Continue to run pump for ten additional minutes.
NOTE: In all evacuating procedures the speci­
fication of 26-28 inches of vacuum is used. This
evacuation can only be attained at or near sea level.
For each 1000 feet above sea level where this
operation is being performed, the specification
should be lowered by one inch of mercury vacuum.
For example: at 5000 feet elevation only 21 to 23
inches of vacuum can normally be obtained.
If vacuum cannot be pulled to the minimum
specification for the respective altitude, it indi­
cates a leak in the system , gauge connections or a
defective vacuum pump. In this case, it will be
necessary to check for leaks as outlined later, after
a small amount of Refrigerant-12 has been added
to the low side of the system .
a. Turn the hand shut-off valves at the low
and high pressure gauge of the gauge set to the
full clockwise position with the vacuum pump oper­
ating, then stop pump.
TO
'C O N D EN SER
-5725-04
, J-6272 -01
T-5939