Filter
Top Products
SCXG-SVX01B-EN 83
Water-cooled: Units without WSE, the
condenser valve modulates to maintain
an average saturated condenser tem-
perature. Units with WSE, if economizing
and mechanical cooling is necessary the
economize valve will sacrifice free
cooling and modulate to maintain
condensing saturated temperature. If not
economizing, the condenser valve will
modulate to maintain condensing
saturated temperature.
Water-cooled units without head pres-
sure control will lock out mechanical
cooling at entering condenser water
temperatures below 54°F. Mechanical
cooling will resume when the entering
condenser water temperature exceeds
58°F.
Low Ambient Control (Air-Cooled Units
Only)
The low ambient modulating output on
the compressor module is functional on
all units with or without the low ambient
option. When the compressor module
stages up to it's highest stage (stage 2 or
3 depending on unit size), the modulating
output is 100% (10 VDC). When the
control is at stage 1, the modulating
output (0-10 VDC) controls the saturated
condensing temperature to within the
programmable condensing temperature
low ambient control point.
Low Ambient Compressor Lockout (Air-
Cooled Units Only)
The low ambient compressor lockout
utilizes an analog input device. When the
system is configured for low ambient
compressor lockout, the compressors will
not operate if the temperature of the
outside air falls below the lockout
setpoint. When the temperature rises 5°F
above the lockout setpoint, the
compressors will operate. The setpoint
for units without the low ambient option is
50°F. For units with the low ambient
option, the setpoint is 0°F. The setpoints
are adjustable at the human interface
panel.
Return Air Temperature Sensor
The return air temperature sensor is an
analog input device used with a return
humidity sensor on units with the
comparative enthalpy option. The sensor
monitors the return air temperature and
compares it to the outdoor temperature
to establish which temperature is best
suited to maintain cooling requirements.
It is mounted in the return air path and
connected to the ECEM.
Supply Fan Circuit Breaker, Fuses, and
Overloads
The supply fan motor is protected by
either circuit breakers fuses or a
combination of fuses and overloads,
dependent upon unit configuration.
Circuit breakers are used on units
without a VFD. They will trip and interrupt
the motor power supply if the current
exceeds the breaker trip value. The RTM
shuts all system functions off when
detecting an open fan proving switch.
Units with a VFD have fuses to protect
the VFD and motor. Units with a VFD w/
bypass have fuses to protect VFD circuit
and overloads to protect the motor when
in bypass.
Supply Air Temperature Low Limit
The supply air temperature low limit
function uses the supply air temperature
sensor input to modulate the economizer
damper to the minimum position if the
supply air temperature falls below the
occupied heating setpoint temperature.
Supply Air Temperature Sensor
The supply air temperature sensor is an
analog input device. It monitors the
supply air temperature for supply air
temperature control, supply air
temperature reset, supply air
temperature low limiting, and supply air
tempering. It is mounted in the supply air
discharge section of the unit and
connected to the RTM.
Supply Airflow Proving Switches
This is binary input device used on units
to signal the RTM when the supply fan is
operating. It is mounted in the supply fan
section and is connected to the RTM.
During a request for fan operation and if
the differential switch opens for 40
consecutive seconds, compressor
operation turns off, heat operation turns
off, the request for supply fan operation is
turns off and locks out, IGV option closes,
economizer damper option closes, and a
manual reset diagnostic initiates.
Low Entering Air Protection Device
(LEATPD)
The low entering air protection device
(LEATPD) is a binary input on units with
hydronic heat or a waterside economizer.
It is optional on water-cooled units.
If the LEATPD is on a unit with factory-
installed heat, it is mounted in the heat
section and connected to the heat
module. If the entering air temperature to
the heating coil falls to 40°F, the normally
open contacts on the LEATPD close and
cause the following events:
a. the hydronic heat actuator fully opens.
b. the supply fan turns off
c. the outside air damper closes
d. the SERVICE light at the remote zone
sensor option turns on.
e. a LEATPD diagnostic displays at the
human interface panel.
If the LEATPD is on a water-cooled unit
without factory-installed heat, it is wired
to the WSM. It will trip if the entering
water temperature falls to 34°F, open the
economizer valve, and energize the
pump output.
High Duct Temp Thermostat Option On
Units with an LCI-I
The high duct temperature thermostats
are binary input devices used on units
with a Trane communication interface
module (Tracer/LCI-I). They provide a high
limit unit shutdown and require a manual
reset. The thermostats are factory set to
open if the supply air temperature
reaches 240°F, or the return air
temperature reaches 135°F. Once tripped,
the thermostat requires a manual reset.
Reset by pressing the sensor’s reset
button when the air temperature
decreases approximately 25°F below the
cutout point.
Filter Switch
The filter switch is a binary input device
that measures the pressure differential
across the unit filters. It is mounted in the
filter section and connected to the RTM. A
diagnostic SERVICE signal displays at the
remote panel if the pressure differential
across the filters is at least 0.5”
w.c. The
contacts automatically open when the
pressure differential across the filters
decrease to
0.4” w.c. The switch
differential is field adjustable between
0.17” to 5.0” w.c. ± 0.05 “.
High Duct Static Switch Option
The high duct static switch is field-
mounted in the ductwork or plenums
with smoke dampers. It will cause a
manual reset diagnostic if the duct static
exceeds the pre-set static limit. The static
limit is adjustable at the HI.
general
information
Operation