Suction Riser; Step 6 - Complete Refrigerant Piping; Connections - Carrier Gemini 38AU07 Series Installation Instructions Manual

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 refrigerant velocity to ensure oil return at mini-
mum load conditions.
38AUZ (ALL) AND 38AUD (A,B) WITHOUT HGBP
Check Table 10 for maximum suction tube size for 38AU
units at minimum load conditions. Consider suction speed ris-
er (reduced tube size for vertical segment only) or double
suction riser arrangement if the planned suction tube size
does not provide necessary minimum flow-rates for this riser.
Table 10 — 38AU Maximum Suction Pipe Size
MODEL UNIT SIZE
38AUZA, B
38AUZD, E
38AUDA, B
38AUDC
38AUDC12 WITH OPTIONAL HOT GAS BYPASS
Special consideration for suction riser requirements must
be considered when applying this factory-installed hot gas
bypass. It is extremely important to consider the lowest possi-
ble refrigerant tons of refrigerant flow when hot gas bypass is
functioning to assure proper oil return up suction risers.
Table 9 provides recommended tube sizes for model
38AUDC12 unit which includes the factory-installed hot gas
bypass system on Circuit 1. The selections in this table are
based on evaluations of system minimum load operating con-
ditions for comfort cooling applications, with compressor sat-
urated suction pressure to 28°F (–2.2°C) minimum.
Table 9 includes liquid line size selections based on use of
RTPF coil option only.
Table 9 includes three different suction line size selections
for Circuit 1 based on the elevation difference conditions be-
tween the 38AUD unit and the evaporator coil location.
Outdoor Unit ABOVE Evaporator Coil
This installation will have at least one suction riser seg-
ment. If the vertical elevation difference is less than 20-ft (6.1
m) linear feet and requires only one or two segments, consid-
er a speed riser selection for Circuit 1; use the line marked
VAPOR RISER REQUIRED; NOT GREATER THAN 20 FT
(6.1 M). See Fig. 5. Tube S is the horizontal line size; tube A
is the reduced diameter riser size.
A
20-FT (6.1 M) MAX
S
LEGEND
A - Suction Riser Without Trap
S - Suction Line to Condensing Unit
Fig. 5 — Suction Line Piping - Speed Riser
If the vertical elevation difference is greater than 20-ft
(6.1-m) linear feet or requires more than two short lift seg-
ments, select the Circuit 1 suction line size from Double
MAXIMUM TUBE SIZE
07 1 3/8
08 1 5/8
12 1 5/8
14 2 1/8
07 1 1/8
12 1 3/8
14 1 5/8
12 See Table 7
CONDENSING
UNIT
Suction Riser lines data under VAPOR RISER 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 without
bottom trap; Tube B is the parallel riser size with bottom oil
trap.
FROM
EVAPORATOR
A - Suction Riser Without Trap
B - Suction Riser With Trap
S - Suction Line to Condensing Unit
Fig. 6 — Suction Line Piping - Double Riser
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
Because there is no hot gas bypass system in Circuit 2, no
special riser selections are necessary. Select Circuit 2 suction
line from bottom line for all 38AUDC installations.
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.
Step 6 — Complete Refrigerant Piping Connec-
tions
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, pur-
chase locally and install locally. Installation will require the re-
covery 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 relief device.
CHECK 38AU MODEL WITH EVAPORATOR COIL

CONNECTIONS

Confirm before installation of unit that the evaporator coil
connections are consistent with this 38AU model. See Table 1
on page 2.
INSULATE SUCTION LINES
Apply closed-cell tubular insulation to all suction lines be-
tween evaporator coil connection and 38AU unit's suction
service valve.
10
A
S
B
S
LEGEND