Komatsu 830E-AC Shop Manual page 961

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
refrigerant has occurred. All these conditions will
require that a vacuum be pulled using a vacuum
pump that completely 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, allow-
ing the water vapor to be easily drawn out by the
pump. The pump does this by reducing the point at
which water boils (100°C, 212°F at sea level with
14.7 psi). In a vacuum, water will boil at a lower tem-
perature depending upon how much of a vacuum is
created.
As an example, if the ambient air outside the truck is
24°C (75°F) at sea level, by creating a vacuum in the
system so that the pressure is below that of the out-
side air (in this case, at least 749.3 mm (29.5 in.) of
vacuum is needed), the boiling point of water will be
lowered to 22°C (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 fol-
lowing steps indicate the proper procedure for evacu-
ating all moisture from the heavy duty air conditioning
systems.
Do not attempt to use the air conditioning com-
pressor as a vacuum pump or the compressor
will be damaged.
NOTE: Refer to Table 2 for optimal vacuum
specifications at various altitudes.
1. With the manifold gauge set still connected
(after discharging the system), connect the cen-
ter hose to the inlet fitting of the vacuum pump
as shown in Figure 4-27. Then open both hand
valves to maximum.
N04031 10/06
2. Open the discharge valve on the vacuum pump
or remove the dust cap from the discharge out-
let. 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. Find the
source of the leak, repair, and attempt to evacu-
ate the system again.
3. Allow the vacuum pump to run for at least 45
minutes.
FIGURE 4-27. VACUUM PUMP HOOKUP
Operator Comfort N4-35