keep the condensing unit service valves
closed and evacuate the suction and liquid
lines and the air handling unit. If the entire
system must be evacuated, use the following
procedure to ensure the entire system is
pulled into a good vacuum.
1. System evacuation must be
performed anytime a system is open to
atmospheric pressure. The POE oils
used with R-410A are extremely
hydroscopic in nature and immediately
begin pulling in moisture once the
system is opened to the atmosphere.
2. Before starting to evacuate the
system, you MUST ensure that there are
no leaks by pressurizing the system with
2758 kpa (400 psig) of dry nitrogen and
verifying no pressure loss after one hour.
3. Four valve manifold gauge sets are
more effective than standard manifold
gauge sets due to the extra hose port in
combination with a 9.5 mm (3/8’’)
evacuation port. The larger diameter
evacuation port will expedite system
evacuation.
4. Connect the manifold set to the
condensing unit with one hose on the
suction line service valve, one hose on
the liquid line service valve and if an
extra Schrader valve is field installed on
the suction line, connect a third hose (not
shown). The vacuum pump must be
connected to the manifold set using a
9.5 mm (3/8”) vacuum rated hose.
Figure 5 shows two circuits. Both
circuits must be evacuated separately.
Figure 5 - CU evacuation connections
5. An accurate micron gauge must be
used and checked by pulling a vacuum
on the gauge by itself and verify a rapid
drop to less than 100 microns within a
few minutes.
6. Do not attach the micron gauge to the
system until the gauge manifold is
reading 71 cm (28”) of vacuum to ensure
the micron gauge does not see pressure
and is thus damaged. MICRON
GAUGES WILL BE DAMAGED BY
PRESSURE!!!
7. It is a good practice to replace the
vacuum pump oil after one hour of the
evacuation process. The oil can be
broken down in the pump in the initial
first hour causing system evacuation to
take longer than it should.
8. The minimum micron level required
by AAON is 350 microns for systems
using POE oils.
9. The system must then be isolated and
the pump turned off to check for vacuum
rise due to leaks or moisture in the
system. The micron gauge must not rise
above 500 microns after 30 minutes of
wait time.
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