Stulz FLAIR series, Installation, Operation And Maintanance Manual

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FLAiR Series Installation, Operation & Maintenance Manual
(©Aug, 2007)
Air Technology Systems, Inc.
2-14
FINE TUNING THE SYSTEM CHARGE
4. Disconnect the refrigerant cylinder from the
discharge side of the compressor and connect it
to the suction side.
5. Start the system and use the microprocessor
controller to lower the temperature setpoint 3-5°F
below room temperature, ensuring cooling
remains on as the unit is charged.
6. Allow the discharge pressure to rise to 225-280
psig and hold it constant. On cool days it may be
necessary to restrict the airflow across the
condenser (or reduce the water/glycol flow), to
raise the pressure.
7. Slowly meter R407C liquid refrigerant through the
suction side while watching the sight glass to clear
of bubbles.
CAUTION
Add liquid refrigerant slowly to prevent the refrig-
erant oil from “washing out” of the compressor.
8. Take a superheat temperature reading on the
suction line near the feeler bulb from the thermal
expansion valve. The ideal superheat temperature
is 12-15°F. The maximum allowable superheat
temperature is 20°F.
9. While monitoring the sight glass, take a sub-
cooling temperature reading on the output side of
the condenser. The sub-cooling temperature
should be 10-20°F.
10. If necessary, add liquid refrigerant to maintain
adequate sub-cooling temperature.
2.8.2.1 Flooded Head Pressure Control Systems
In units with R407C refrigerant using flooded head
pressure control, a receiver is provided to store the
refrigerant during the time the condenser is not using
the extra refrigerant charge. Once a clear sight glass
has been achieved, additional refrigerant must be
added to the receiver.
A level indicator (sight glass), is located on the side of
the receiver to assist the service technician in charg-
ing the air conditioning system. The proper charge
can be determined by viewing the position of the “float
constant, however, the refrigerant vapor tends to
separate into its component parts even when circulat-
ing. When charging a system using a blended
refrigerant, it is essential that the composition of the
refrigerant is maintained. To ensure correct composi-
tion, introduce R407C into the system in liquid form
rather than vapor form. Cylinders which are not
provided with dip tubes should be inverted to allow
only
liquid refrigerant to charge the system. Keeping
the temperature of the cylinder below 85°F will help to
maintain the correct refrigerant composition while the
cylinder is emptied.
CAUTION
POE oil is used in systems with R407C refrigerant.
POE oil quickly absorbs moisture when exposed to
air. High POE oil moisture levels react with refrigerant
to form acid, which results in system contamination.
Keep the entire system sealed as much as possible
and minimize exposure of the POE oil to outside air.
Familiarize yourself with the charging procedures
discussed in section 2.8.1 of this manual. Instead of
adding R22 vapor to the suction port as described
under “Preparing System for Charging”, the initial
charge will be performed by introducing R407C
liquid
to the discharge side of the compressor. (See below)
PREPARING SYSTEM FOR CHARGING
1. With all the system piping connections made,
perform a dry nitrogen leak detection test on the
system. Using dry nitrogen only
, pressurize the
system to 150 psig. Since there is no refrigerant
in the system to detect, leaks may be detected
by observing the standing pressure.
2. After ensuring there are no leaks, evacuate the
system to 50 microns and hold the vacuum for 2
hours.
3. Break the vacuum by supplying R407C liquid to
the discharge port near the compressor until the
pressure is raised to about 50 psig. This small
holding charge allows the low pressure switch to
“make” through the process of fine tuning the
system charge.