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Suction Riser
A suction riser condition exists when the outdoor unit is located
above the indoor (evaporator) unit and suction vapor must flow
vertically up to return to the compressor. Oil return is a concern
when the suction tube size is too large to produce the minimum re-
frigerant velocity to ensure oil return at minimum load conditions.
38AUZ AND 38AUD
Check Table 9 for maximum suction tube size for 38AU units at
minimum load conditions. Consider suction speed riser (reduced
tube size for vertical segment only) or double suction riser ar-
rangement if the planned suction tube size does not provide neces-
sary minimum flow-rates for this riser.
Table 9 — 38AU Maximum Suction Pipe Size
MODEL
UNIT SIZE
38AUZ
16/25
38AUD
16/25/28
Outdoor Unit ABOVE Evaporator Coil
This installation will have at least one suction riser segment. If the
vertical elevation difference is less than 20-ft (6.1 m) linear feet
and requires only one or two segments, consider a speed riser
selection for Circuit 1; use the line marked VAPOR RISER RE-
QUIRED; NOT GREATER THAN 20 FT (6.1 M). See Fig. 6.
Tube S is the horizontal line size; tube A is the reduced diameter
riser size.
If the vertical elevation difference is greater than 20-ft (6.1-m) lin-
ear feet or requires more than two short lift segments, select the
Circuit 1 suction line size from Double Suction Riser lines data
under VAPOR RISER GREATER THAN 20 FT (6.1 M). See
Fig. 7. Tube S is the horizontal line size. Tube A is the reduced di-
ameter riser size without bottom trap; Tube B is the parallel riser
size with bottom oil trap.
Outdoor Unit BELOW Evaporator Coil and No Vertical Riser
Segments
Select Circuit 1 suction line size from NO VAPOR RISER line.
Circuit 2 Suction Line
No special riser selections are necessary.
Vertical Separation (outdoor unit above indoor unit)
Vertical elevation difference of 200 ft (60 m) is permitted when
the outdoor unit (38AUZ or 38AUD) is located above the indoor
unit.
A
S
LEGEND
A - Suction Riser With Trap
S - Suction Line to Condensing Unit
Fig. 6 — Suction Line Piping — Speed Riser
MAXIMUM TUBE SIZE (in.)
1-5/8
1-5/8
Condensing
Unit
20-ft (6.1 m)
max
A
S
From
Evaporator
LEGEND
A - Suction Riser Without Trap
B - Suction Riser With Trap
S - Suction Line to Condensing Unit
Fig. 7 — Suction Line Piping — Double Riser
Step 6 — Complete Refrigerant Piping
Connections
IMPORTANT: DO NOT BURY REFRIGERANT LINES.
IMPORTANT: A refrigerant receiver is not provided with the
unit. Do not install a receiver.
PROVIDE SAFETY RELIEF
If local codes dictate an additional safety relief device, purchase
locally and install locally. Installation will require the recovery
of the factory shipping charge before the factory tubing can be
cut and the supplemental relief device is installed.
Model 38AUD has two separate refrigeration systems. If required,
each circuit will require a field-supplied/installed supplemental re-
lief device.
CHECK 38AU MODEL WITH EVAPORATOR COIL
CONNECTIONS
Confirm before installation of unit that the evaporator coil con-
nections are consistent with this 38AU model. See Table 3 on
page 3.
INSULATE SUCTION LINES
Apply closed-cell tubular insulation to all suction lines between
evaporator coil connection and 38AU unit's suction service valve.
38AUD PIPING CONNECTIONS
The 38AUD unit's two circuits are designated Circuit 1 and
Circuit 2. Circuit 1 is controlled by the thermostat's Y1 (or TC1)
contact and will be the first circuit on and last circuit off. Circuit 2
is controlled by the thermostat's Y2 (or TC2) contact and this cir-
cuit is always the "lag" circuit.
See Fig. 8 for location of Circuit 1 and Circuit 2 service valves and
field piping connections. Circuit 1 is on the right-hand side of the
service valve compartment; Circuit 2 is on the left.
11
S
B
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