13
Evaporator Capacity Control Liquid Line Solenoid Valve
Many older unit designs included automatic capacity controls
that sensed changes in suction pressure and could increase 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 connection to the
compressor circuit.
This form of system capacity staging control is not possible with
38AU models. If this installation is a retrofit for a unit that includ-
ed automatic pressure-operated unloading, check the existing ther-
mostat and liquid solenoid valve. When found, convert the evapo-
rator 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 accumulator
is not required. If an accumulator is to be added, check the accu-
mulator manufacturer’s literature carefully for indication of its
suitability for use with R-410A; look for minimum working pres-
sure of 200 psig (1380 kPa). Select the accumulator first on the ba-
sis 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 intercon-
necting tube brazing has been completed. The stub tube connec-
tions include
1
/
4
-in. SAE service fittings with 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).
Fig. 11 — Typical Piping Connection Assembly
EVACUATION/DEHYDRATION
Evacuate and dehydrate the connected refrigeration system(s) (ex-
cluding 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.
This unit is designed for use with Puron (R-410A) refrigerant. Do
not use any other refrigerant in this system.
Puron (R-410A) refrigerant is provided in pink (rose) colored cyl-
inders. These cylinders are available with and without dip tubes;
cylinders with dip tubes will have a label indicating this feature.
For a cylinder with a dip tube, place the cylinder in the upright po-
sition (access valve at the top) when removing liquid refrigerant
for charging. For a cylinder without a dip tube, invert the cylinder
(access valve on the bottom) when removing liquid refrigerant.
Because Puron (R-410A) refrigerant is a blend, it is strongly rec-
ommended that refrigerant always be removed from the cylinder
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
cylinder 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 service valve(s).
The amount of refrigerant added must be at least 80% of the oper-
ating charge listed in Tables or 6 for LINEAR 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 man-
ifold 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 Reclama-
tion 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 8 (38AUZ):
Liquid
1
/
2
in.
Suction 1
1
/
8
in.
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
Step 7 — Install Accessories
Accessories requiring modifications to unit wiring should be com-
pleted now. These accessories may include Winter Start controls
and Low Ambient controls. Refer to the instructions shipped with
the accessory.
FACTORY
HIGH-FLOW
ACCESS PORT
SERVICE VALVE
WITH STEM CAP
FIELD SERVICE
ACCESS PORT
(SCHRADER CORE)
SWEAT
CONNECTION
WARNING
UNIT OPERATION AND SAFETY HAZARD
Failure to follow this warning could cause personal injury,
death and/or equipment damage.
R-410A refrigerant systems operate at higher pressures than
standard R-22 systems. Do not use R-22 service equipment or
components on R-410A refrigerant equipment.
