Komatsu 930E-2, Shop Manual

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EVACUATING THE SYSTEM
Evacuating the complete air conditioning system is
required in all new system installations, and when
repairs are made on systems requiring a component
replacement (system opened), or a major loss of refrig-
erant has occurred. All these conditions will require that
a vacuum be pulled using a vacuum pump that com-
pletely removes any moisture from the system. Once
properly evacuated, the system can be recharged
again.
Using a pump to create a vacuum in the air condition-
ing system effectively vaporizes any moisture, allowing
the water vapor to be easily drawn out by the pump.
The pump does this by reducing the point at which
water boils (212°F at sea level with 14.7 psi). In a
vacuum, water will boil at a lower temperature depend-
ing upon how much of a vacuum is created.
As an example, if the ambient air outside the truck is
75°F at sea level, by creating a vacuum in the system
so that the pressure is below that of the outside air (in
this case, at least 29.5 inches of vacuum is needed),
the boiling point of water will be lowered to 72°F. Thus
any moisture in the system will vaporize and be drawn
out by the pump if the pump is run for approximately
an hour. The following steps indicate the proper pro-
cedure for evacuating all moisture from the heavy duty
air conditioning systems.
Do not use the air conditioning compressor as a
vacuum pump or the compressor will be damaged.
NOTE: Lower the vacuum requirement one inch for
every 1000 feet above sea level at your location.
1. With the manifold gauge set still connected (after
discharging the system), connect the center hose
to the inlet fitting of the vacuum pump as shown
in Figure 9-10. Then open the low side hand valves
to maximum.
2. Open the discharge valve on the vacuum pump or
remove the dust cap from the discharge outlet.
Turn the pump on and watch the low side gauge.
The pump should pull the system into a vacuum
(if not, the system has a leak).
3. Run the pump for five minutes and close the hand
valves and shut off the pump.
4. Observe gauge reading and wait 10 minutes.
Reading should not vary more than 1-2 in. hg.
After waiting, if more vacuum is lost than this, a
serious leak is indicated and the system must be
recharged, leak tested, repaired and evacuated.
5. Turn on pump, open hand valves and continue
evacuation for at least one hour.
NOTE: If system has excessive amounts of moisture,
60 minutes evacuation may not be sufficient since the
water must turn to a vapor to be drawn out of the
system. If it has been verified that no system leaks exist
and gauge readings increase after 1 hour, extend the
evacuation time to ensure total moisture removal.
6. Close the manifold hand valves and turn off vac-
uum pump, watching the low side gauge reading.
If vacuum remains for a few minutes, the system
is ready for charging.
NOTE: If using a recycling and charging machine, the
vacuum pump is built into the unit. Separate hook-up
is not required.
FIGURE 9-10. VACUUM PUMP HOOKUP
1. Low Pressure Hand Valve
2. High Pressure Hand Valve 3. Vacuum Pump
M9-18 Air Conditioning System M09010 6/97
for HFC 134a Refrigerant