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90 SCXG-SVX01B-EN
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 to 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 VFDs.
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 VFDs
have fuses to protect the VFD and motor.
Units with 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
The low entering air protection device
(LEATPD) is a binary input on units with
hydronic heat or a waterside economizer.
It is optional on all 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 a TCI
The high duct temperature thermostats
are binary input devices used on units
with a Trane communication interface
module (TCI). The high duct temperature
thermostat provides a high limit unit
shutdown and requires 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
used on units to measure 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 preset static limit. The static limit is
adjustable at the HI.
Owner
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