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Mount the SVR (and transformer TRAN3 when used) in
unit control box. Connect per wiring schematic label on unit.
NOTE: TRAN3 is provided with the HGBP factory installed op-
tion for 38AUDC12 units.
Evaporator Capacity Control Liquid Line Solenoid Valve
Many older unit designs included automatic capacity con-
trols that sensed changes in suction pressure and could in-
crease or decrease compressor capacity automatically as the
evaporator load changed. Control systems were used on these
units that had the thermostat's second stage contacts control a
capacity control liquid line solenoid valve to open or shutoff
a portion of the evaporator surface without any direct connec-
tion to the compressor circuit.
This form of system capacity staging control is not possi-
ble with 38AU models. If this installation is a retrofit for a
unit that included automatic pressure-operated unloading,
check the existing thermostat and liquid solenoid valve.
When found, convert the evaporator second stage solenoid
control into a drop-solenoid control. Use the two SVR relays
and transformer as required on 38AUD models (above); wire
the SVRs and transformer per two solenoid valve systems.
SELECTING AN ACCUMULATOR
Because all 38AU models use scroll compressors, an accu-
mulator is not required. If an accumulator is to be added,
check the accumulator manufacturer's literature carefully for
indication of its suitability for use with R-410A; look for
minimum working pressure of 200 psig (1380 kPa). Select
the accumulator first on the basis of its cataloged minimum
capacity (tons) to ensure oil return from the accumulator, then
on tube size or holding capacity.
MAKE PIPING CONNECTIONS
Piping connections at the 38AU unit are ball valves with
stub tube extensions. Do not open the unit service valves until
all interconnecting tube brazing has been completed. The stub
tube connections include
Schrader valve cores (see Fig. 11). Before making any brazed
connections to the unit service valves, remove both Schrader
valve caps and cores and save for re-installation. Connect a
source for nitrogen to one of these service fittings during tube
brazing to prevent the formation of copper oxides inside the
tubes at brazed joints.
When connecting the field tubing to the 38AU service
valves, wrap the valves in wet rags to prevent overheating.
Pressure-test all joints from outdoor unit connections over
to the evaporator coil, using nitrogen as pressure and with
soap-and-bubbles.
When pressure-testing is completed, remove the nitrogen
source at the outdoor unit service valves and re-install the
two Schrader valve cores. Torque the cores to 2-3 in.-lbs
(23-34 N-cm).
FACTORY
HIGH-FLOW
ACCESS PORT
SERVICE VALVE
WITH STEM CAP
Fig. 11 — Typical Piping Connection Assembly
1
/
-in. SAE service fittings with
4
FIELD SERVICE
ACCESS PORT
(SCHRADER CORE)
SWEAT
CONNECTION
EVACUATION/DEHYDRATION
Evacuate and dehydrate the connected refrigeration sys-
tem(s) (excluding the 38AU unit) to 500 microns using a two-
stage vacuum pump attached to the service ports outside the
38AU service valves, following description in GTAC II,
Module 4, System Dehydration.
UNIT OPERATION AND SAFETY HAZARD
Failure to follow this warning could cause personal injury,
death and/or equipment damage.
Puron (R-410A) refrigerant systems operate at higher pres-
sures than standard R-22 systems. Do not use R-22 service
equipment or components on Puron refrigerant equipment.
This unit is designed for use with Puron (R-410A) refrig-
erant. Do not use any other refrigerant in this system.
Puron (R-410A) refrigerant is provided in pink (rose) col-
ored cylinders. These cylinders are available with and with-
out dip tubes; cylinders with dip tubes will have a label indi-
cating this feature. For a cylinder with a dip tube, place the
cylinder in the upright position (access valve at the top) when
removing liquid refrigerant for charging. For a cylinder with-
out a dip tube, invert the cylinder (access valve on the bot-
tom) when removing liquid refrigerant.
Because Puron (R-410A) refrigerant is a blend, it is strongly
recommended that refrigerant always be removed from the cyl-
inder as a liquid. Admit liquid refrigerant into the system in the
discharge line. If adding refrigerant into the suction line, use a
commercial metering/expansion device at the gauge manifold;
remove liquid from the cylinder, pass it through the metering
device at the gauge set and then pass it into the suction line as a
vapor. Do not remove Puron (R-410A) refrigerant from the cyl-
inder as a vapor.
PRELIMINARY CHARGE
Before starting the unit, charge R-410A liquid refrigerant
into the high side of each 38AU circuit through the liquid ser-
vice valve(s). The amount of refrigerant added must be at
least 80% of the operating charge listed in Table 6 for LIN-
EAR line length LESS the factory charge quantity (if factory
shipping charge has not been removed). See example below.
Allow high and low side pressures to equalize. If pressures
do not equalize readily, charge R-410A vapor (using special
service manifold with expansion device) into the suction line
service port for the low side of system to assure charge in the
evaporator. Refer to GTAC II, Module 5, Charging, Recover,
Recycling, and Reclamation for liquid charging procedures.
Example:
38AUZ*12
60-ft (18.3 m) linear line length
Equivalent line length 90-ft (27.4 m)
Liquid Lift: 20-ft (6.1 m)
Select line sizes from Table 7 (38AUZ):
Liquid
/
in.
1
2
Suction 1
1
/
in.
8
Charge 23.1 lbs (at 75-ft linear length)
80% of Operating Charge:
0.80 x 23.1 = 18.5 lbs
Factory Shipping Charge: 9 lbs
Field-Charge quantity: 18.5 - 9.0 = 9.5 lbs
For linear line lengths longer than 125 ft (38 m), contact
your local Carrier representative for system charge value.
13
WARNING
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