Trane IntelliPak SCRF 25, Installation, Operation And Maintenance Manual

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SCXF-SVX01Q-EN 77
temperature. If not economizing, the condenser valve
will modulate to maintain condensing saturated
temperature. Water-cooled units without head pressure
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 stages 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
Utilizes an analog input device. When the system is
configured for low ambient compressor lockout, the
compressors are not allowed to 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 are allowed to
operate. The factory preset is 50°F.
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
Uses the supply air temperature sensor input to
modulate the economizer damper to minimum position
in the event 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 turns off and locks out,
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:
• The hydronic heat actuator fully opens.
• The supply fan turns off
• The outside air damper closes
• The SERVICE light at the remote zone sensor option
turns on.
• 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).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
A binary input device that measures the pressure
differential across the unit filters. It is mounted in the
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