21
Low Ambient & Modulating Reheat
System Evacuation Instructions:
Proper system evacuation is critical to
remove moisture and non-condensables from
the system before charging the system with
refrigerant. Systems with low ambient
flooded condenser option require 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. Open the reheat valve to 50% when
evacuating.
3. 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.
4. 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.
5. 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 a third
hose on the reheat line service valve.
The vacuum pump must be connected to
the manifold set using a 9.5 mm (3/8”)
vacuum rated hose. Figure 6 shows two
circuits. The first circuit has a reheat
line, the second circuit is just the suction
and liquid line. Both circuits must be
evacuated separately.
6. FAILURE to connect to the liquid
line service valve will result in the
receiver tank not being fully evacuated
and most likely lead to non-
condensables in the system.
7. 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.
Figure 6 - CU evacuation connections
8. 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!!!
9. It is a good practice to replace the
vacuum pump oil after one hour of the
evacuation process. The oil can be
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