Carrier 38AU - Manual (Page 12)

12
INSULATE SUCTION LINES — Apply closed-cell tubular
insulation to all suction lines between evaporator coil
connection and 38AU unit’s suction service valve.
Hot Gas Bypass – Hot gas bypass, if used, should be
introduced before the evaporator. (A bypass route that also
bypasses the evaporator circuit may lead to oil trapping in the
evaporator circuit during low load conditions and then to oil
slugging as evaporator load increases.) Model 38AU units do
not include a hot gas stub connection; a tee must be field-
supplied and installed in the compressor discharge line. Run a
½-in OD line between outdoor unit and evaporator coil inlet.
Install an Auxiliary Side Connector at the evaporator between
TXV and distributor (follow instructions for the side connector
part). Insulate the hot gas line.
38AUD: Generally only one hot gas bypass system will be
applied on a two-circuit unit. Connect the hot gas bypass
system to Circuit A (first-on/last-off, connected to the
evaporator coil’s bottom circuit).
38AUD PIPING CONNECTIONS – The 38AUD’s two
circuits are designated Circuit A and Circuit B. Circuit A is
controlled by the thermostat’s Y1 (or TC1) contact and will be
the first circuit on and last circuit off. Circuit B is controlled by
the thermostat’s Y2 (or TC2) contact and this circuit is always
the “lag” circuit.
See Fig. 5 for location of the Circuit A and Circuit B service
valves and field piping connections. Circuit A is on the right-
hand side of the service valve compartment; Circuit B is on the
left.
Fig 5 - 38AUD Service Valve Locations
When a single piece evaporator coil with two separate circuits
is connected to a 38AUD, the lower coil circuit should be
connected to the 38AUD’s Circuit A so that the evaporator’s
lower coil segment is first-on/last-off (to avoid re-evaporation
of condensate on dry lower coil segments).
Plan the Circuit A and Circuit B tubing segments carefully,
mark each segment and check constantly as piping systems are
assembled to avoid piping errors.
38AUD unit cannot be field-piped as a single-circuit/tandem
system.
Connecting 40RU to 38AUD – The 40RU fan coil in sizes 12,
14 and 16 is a face-split coil design that also has its circuits
designated as A and B. See Fig. 6. Note that the lower coil
segment changes as the arrangement of the 40RU changes. In a
vertical arrangement, the 40RU’s lower coil segment is
segment B; this segment should be connected to the 38AUD’s
Circuit A. In a horizontal arrangement, the 40RU’s lower
segment is now segment A; this segment should be connected
to the 38AUD’s Circuit A.
Fig. 6 — Typical Evaporator Coil Connections (40RU)
Note that refrigerant suction piping should be insulated.
INSTALL FILTER DRIER(S) AND MOISTURE
INDICATOR(S) — Every unit MUST have a filter drier in the
liquid line. 38AUD models require two filter driers (one in
each liquid line). Locate the filter drier(s) at the indoor unit,
close to the evaporator coil’s thermal expansion valve (TXV)
inlets.
38AU units include one (38AUZ) or two (38AUD) Puron-duty
filter drier(s), shipped in cartons attached to the unit basepan.
Remove the filter drier(s) and prepare to install in the liquid
line(s) at the evaporator coil. Do not remove connection fitting
plugs until ready to connect and braze the filter drier into the
liquid line position.
Table 8 — Puron-duty Filter Drier(s)
Installation of liquid line moisture indicating sightglass in each
circuit is recommended. Locate the sightglass(es) between the
outlet of the filter drier and the TXV inlet.
Circuit A
Connections
Circuit B
Connections
40RU
Arrangement
Cooling
Stage
40RU Coil
Segment
Connect to
38AUD
Vertical
Y1
Y2
B
A
Circuit A
Circuit B
Horizontal
Y1
Y2
A
B
Circuit A
Circuit B
Model-Size Qty
Liquid
Line OD
Desiccant
Volume
Part
Number Ref
38AUZ*07 1 3 /
8
-in 8 cu. in. KH43LG091
38AUZ*08 1 1 /
2
-in 16 cu. in. KH43LG085
38AUD*12 2 3 /
8
-in 8 cu. in. KH43LG091
38AUD*14 2 1 /
2
-in 16 cu. in. KH43LG085
FIRST ON/LAST OFF = B
VERTICAL INSTALLATION
FIRST ON/LAST OFF = A
HORIZONTAL INSTALLATION