General Information
RT-SVX24J-EN
15
For evaporative condensing units, head pressure is
monitored with pressure transducers attached to the
saturated condensing line and converted to a temperature
by the MPM. This temperature is used to control the
variable speed fan and sump pump. When the
temperature rises above the upper limit (120°F) the sump
pump is energized. If the condensing temperature drops
below the lower limit (70°F) the sump pump is de-
energized.
High Pressure Limit Controls
High Pressure controls are located on the discharge lines
near the scroll compressors. They are designed to open
when the discharge pressure approaches 650 ± 10 psig.
The controls reset automatically when the discharge
pressure decreases to approximately 550 ± 10 psig.
However, the compressors on that circuit are locked out
and a manual reset diagnostic is initiated after the fourth
occurrence of a high pressure condition.
Outdoor Air Humidity Sensor
An analog input device used on CV and VAV applications
with 100% economizer. It monitors the outdoor humidity
levels for economizer operation. It is mounted in the
outside air intake section and is connected to the RTM.
Return Air Humidity Sensor
An analog input device used on CV and VAV applications
with the comparative enthalpy option. It monitors the
return air humidity level and compares it to the outdoor
humidity level to establish which conditions are best
suited to maintain the cooling requirements. It is mounted
in the return air section and is connected to the ECEM.
Space Humidity Sensor
Analog input device used on CV andVAV applications with
modulating dehumidification option and/or
humidification field installed option. It is used to monitor
the humidity level in the space and compared to
dehumidification and humidification setpoints to maintain
space humidity requirements. It is field mounted in the
space and connected to the RTM.
Status/Annunciator Output
An internal function within the RTM module on CV and
VAV applications that provides:
c. diagnostic and mode status signals to the remote
panel (LEDs) and to the Human Interface
d. control of the binary Alarm output on the RTM
e. control of the binary outputs on the GBAS module
to inform the customer of the operational status
and/or diagnostic conditions
Low Ambient Compressor Lockout
Utilizes an analog input device for CV and VAV
applications. 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.
These compressors come equipped with a protection
module that monitors phase loss, phase sequencing and
motor temperature.
Space Pressure Transducer
An analog input device used on CV and VAV applications
with the Statitrac option. It modulates the exhaust
dampers to keep the space pressure within the building to
a customer designated controlband. It is mounted on the
bottom support below the return damper blade assembly
and is connected to the ECEM. Field supplied pneumatic
tubing must be connected between the space being
controlled and the transducer assembly.
Morning Warm-Up—Zone Heat
When a system changes from an unoccupied to an
occupied mode, or switches from STOPPED to AUTO, or
power is applied to a unit with the MWU option, the heater
in the unit or external heat will be brought on if the space
temperature is below the MWU setpoint. The heat will
remain on until the temperature reaches the MWU
setpoint.
If the unit is VAV, then the VAV box/unocc relay will
continue to stay in the unoccupied position and the VFD
output will stay at 100% during the MWU mode. When the
MWU setpoint is reached and the heat mode is terminated,
then the VAV box/unocc relay will switch to the occupied
mode and the VFD output will be controlled by the duct
static pressure. During Full Capacity MWU the economizer
damper is held closed for as long as it takes to reach
setpoint. During Cycling Capacity MWU the economizer
damper is allowed to go to minimum position after one
hour of operation if setpoint has not been reached.
Compressor Motor Winding Thermostats
A thermostat is embedded in the motor windings of each
Scroll compressor. Each thermostat is designed to open if
the motor windings exceed approximately 221°F. The
thermostat will reset automatically when the winding
temperature decreases to approximately 181°F.
Rapid cycling, loss of charge, abnormally high suction
temperatures, or the compressor running backwards
could cause the thermostat to open. During a request for
compressor operation, if the Compressor Module detects
a problem outside of normal parameters, it turns any
operating compressor(s) on that circuit “Off”, locks out all
compressor operation for that circuit, and initiates a
manual reset diagnostic (compressor trip).
These compressors come equipped with a protection
module that monitors phase loss, phase sequencing and
motor temperature.
