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Unit Airside Components
The air delivery system consists of dampers, enthalpy
switch option, airside economizer option, filters, low
ambient sensors, and factory mounted single or double
wall plenums.
Supply Air Fan
The unit has two supply fans on a single shaft that run
at a constant speed (CV). However, the fans may have
Table 37. Supply fan horsepower selections
Unit Model
SXRF
SXWF
20, 22, 25
25, 29
29, 32
30, 35
35, 38
42, 46
40
52, 58, 65
50
72, 80
60
90, 100, 110
Low Entering Air Temperature Sensor
This is standard on all units with a hydronic coil or
waterside economizer. It can also be ordered as an
option.
A thermostat limit switch is factory mounted on the
entering air side of the unit with a capillary tube
serpentine across the coil face. If the temperature falls
below 35°F (2°C), the fan shuts down and the waterside
economizer and/or hydronic heat valve options open to
allow full water flow. The heat output also energizes. A
manual reset is required. The low entering air
temperature setpoint is adjustable at the HI.
High Duct Temperature Thermostat
A factory-supplied temperature limit switch with reset
element detects the supply air duct temperature. This
sensor should be field-installed downstream from the
discharge in the supply air duct. If the supply air duct
temperature exceeds 240°F (115.6°C), the unit shuts
down and displays a diagnostic. A manual reset is
required at the unit. High duct temperature can be
adjusted at thermostat.
Dirty Filter Sensor Option
A factory installed pressure switch senses the pressure
differential across the filters. When the differential
pressure exceeds 0.9 inches (23 mm) WG, contact
closure occurs and the HI will display a diagnostic. The
unit will continue to run until you replace the air filters.
A field installed indicator device may be wired to relay
terminals to indicate when filter service is required.
SCXF-SVX01Q-EN
5
7.5
10
15
X
X
X
X
X
X
X
X
X
X
X
X
X
the VFD option with supply air temperature control
(VAV) that modulates airflow based on supply air duct
static pressure. Pressing the stop key on the HI will turn
the supply fan off. The fan is on continuously when a
CV unit is in occupied mode and except when a unit is
in the night heat/morning warm-up mode. During the
night heat and setback mode the fan cycles on and off
in response to a call for heat.See supply fan table
below for available fan horsepower.
HP
20
25
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Contacts are rated at 115 VAC and are powered by a
field-supplied transformer.
Low Ambient Sensor (Air-Cooled Units)
Low ambient sensor is field-installed on air-cooled
units. Position it in a location subject to ambient
temperatures only and not exposed to direct sunlight
or exhaust fans.
The low pressure cutout initiates based on the ambient
temperature. A time delay on the low pressure cutout
initiates for ambient temperatures between 50 (zero
minutes) and 0°F (10 minutes).This helps to prevent
nuisance low pressure cutout trips.
Supply Air Static Pressure Limit
The opening of the VAV boxes coordinate during unit
startup and transition to/from occupied/unoccupied
modes to prevent supply air duct over pressurization.
However, if for any reason the supply air pressure
exceeds the user-defined supply air static pressure
limit set at the HI panel, the supply fan VFD shuts
down. The unit will attempt to restart, up to three
times. If the over pressurization condition still occurs
on the third restart, the unit shuts down and a manual
reset diagnostic sets and displays at the HI.
Variable Frequency Drive Option
Variable frequency drive (VFD) is driven by a
modulating 0-10 vdc signal from the RTM module. A
pressure transducer measures duct static pressure, and
the VFD adjusts fan speed to maintain the supply air
O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
30
40
50
X
X
X
X
X
X
X
X
X
60
X
65
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