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www.DaikinApplied.com 31
IM 893-10 • ROOFPAK SINGLEZONE UNITS
Holding Charge
WARNING
Before applying heat to remove brazed piping caps and plugs,
always vent piping to atmosphere. Failure to do so can cause
hazardous pressures, explosion, severe personal injuries, or
death.
The RFS unit and RCS unit ship with a nitrogen holding
charge. At the time the unit was received, a visual inspection of
the unit piping should have been made to be sure no breakage
had occurred or that the fittings had not loosened. A pressure
test on the RCS units should indicate a positive pressure
in the unit. If no pressure is evident, the unit will have to be
leak tested and the leak repaired. This should be noted and
reported to the Daikin sales representative and freight carrier if
the loss is due to shipping damage.
RCS
—Vent to atmosphere by opening gauge ports at the
compressors and liquid line charging valves.
RFS
—Vent to atmosphere by cutting off the process tubes on
the suction line caps.
The RFS unit does not have gauge ports for pressure
measurement. If no positive pressure is detected when
cutting off the process tubes and removing the tubing caps,
the unit should be leak tested as scribed below, after the
interconnecting piping has been brazed in place. This test will
also confirm the integrity of the field braze joints.
Leak Testing
WARNING
Do not use oxygen or air to build up pressure. Explosion
hazard can cause severe personal injury or death.
In the case of loss of the nitrogen holding charge, the unit
should be checked for leaks prior to charging the complete
system. If the full charge was lost, leak testing can be done
by charging the refrigerant into the unit to build the pressure
to approximately 10 psig by adding sufficient dry nitrogen to
bring the pressure to a maximum of 125 psig. The unit should
then be leak tested with halide or electronic leak detector. After
making any necessary repair, the system should be evacuated
as described.
Evacuation
After determining the unit is tight and there are no refrigerant
leaks, evacuate the system. Use a vacuum pump with a
pumping capacity of approximately 3 cu.ft./min. and the ability
to reduce the vacuum in the unit to at least 1 mm (1000
microns).
1. Connect a mercury manometer or an electronic or other
type of micron gauge to the unit at a point remote from
the vacuum pump. For readings below 1 millimeter, use
an electronic or other micron gauge.
2. Use the triple evacuation method, which is particularly
helpful if the vacuum pump is unable to obtain the
desired 1 mm of vacuum. The system is first evacuated
to approximately 29ʺ (740 mm) of mercury. Then add
enough refrigerant vapor to the system to bring the
pressure up to 0 pounds (0 microns).
3. Evacuate the system again to 29ʺ (740 mm) of vacuum.
Repeat his procedure three times. This method
is most effective by holding system pressure at 0
pounds (0 microns) for a minimum of 1 hour between
evacuations. The first pulldown removes about 90% of
the noncondensables; the second removes about 90%
of that remaining from the first pulldown. After the third
pulldown, only 1/10 of 1% of noncondensables remains.
shows the relationship between pressure, microns,
atmospheres, and the boiling point of water.
CAUTION
To prevent liquid return and damage to the compressor on
systems with optional hot gas bypass, locate the bypass
solenoid valve on the RCS, not on the RFS unit.
CAUTION
Before replacing refrigerant sensors or protective devices, see
prevent an abrupt loss of the entire charge.
CAUTION
Refrigerant charge in the system typically exceeds the
capacity of the microchannel condenser. Removal of the
refrigerant is required to service refrigerant components.
Compressors can be isolated from the system if optional
service valves are installed in the discharge and suction lines.
