11
Generally only one hot gas bypass system will be applied
on a two-circuit unit. Connect the hot gas bypass system
to Circuit 1 (first-on/last-off, connected to the evaporator
coil’s bottom circuit).
38AUD PIPING CONNECTIONS – The 38AUD’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 circuit is always the “lag” circuit.
See Fig. 6 for location of Circuit 1 and Circuit 2 service
valves and field piping connections. Circuit 1 is on the
left-hand side of the service valve compartment; Circuit 2 is
on the right.
Circuit A
Connections
Circuit B
Connections
C10070
Fig. 6 -- 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 1 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 1 and Circuit 2 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
16, 25 and 28 is a face-split coil design that also has its
circuits designated as 1 and 2. See Fig. 7. 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 2; this segment should be connected to
the 38AUD’s Circuit 1. In a horizontal arrangement, the
40RU’s lower segment is now segment 1; this segment
should be connected to the 38AUD’s Circuit 1.
Note that refrigerant suction piping should be insulated.
40RU
Arrangement
Cooling
Stage
40RU C oil
Segment
Connect to
38AUD
Vertical
Y1
Y2
2
1
Circuit 1
Circuit 2
Horizontal
Y1
Y2
1
2
Circuit 1
Circuit 2
FIRST ON/LAST OFF = 2
VERTICAL INSTALLATION
FIRST ON/LAST OF F = 1
HORIZONTAL INSTALLATION
1
2
2
1
C10071
Fig. 7 -- Typical Evaporator Coil Connections (40RU)
INSTALL FILTER DRIERS AND MOISTURE
INDICATORS — 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 driers at the
indoor unit, close to the evaporator coil’s thermal
expansion valve (TXV) inlets.
38AUD units include two Puron-duty filter driers, shipped
in cartons attached to the unit basepan. Remove the filter
driers and prepare to install in the liquid lines 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 6 – Puron-duty Filter Driers
Model-Size Qty
Liquid
Line OD
Desiccant
Volume
Part
Number Ref
38AUD*16 2
1
/
2
-in 16 cu. in. KH43LG085
38AUD*25 2
1
/
2
-in 16 cu. in. KH43LG085
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.
Refer to Table 7 for recommendations on refrigeration
specialties.
38AUD
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