Trane IntelliPak Installation, Operation And Maintenance Manual page 16

General Information
each refrigeration circuit. On 40 - 89Ton units only the
compressor banks will switch, not the order the
compressors within a bank, providing the first compressor
in each circuit had been activated during the same request
for cooling. Lead lag is not available with variable speed
compressor.
Supply and Exhaust/Return Fan Circuit
Breakers (with 1CB1 and 1CB2)
The supply fan and exhaust fan motors are protected by
circuit breakers 1CB1 and 1CB2 respectively for 208 -230V
applications.They will trip and interrupt the power supply
to the motors if the current exceeds the breaker's "must
trip" value. For 460 -575 V applications, fan motors will be
protected with manual motor protectors.The rooftop
module (RTM) will shut all system functions "Off" when an
open fan proving switch is detected.
Manual Motor Protectors (380V through 575V
Only)
Manual motor protectors will be used as branch circuit
protection for compressors and supply fan motors.These
devices are capable of providing both overload and short-
circuit protection. Before operating, the manual motor
protector must be switched with the rotary on/off switch to
the "ON" position and the overload setpoint dial must be
set to the appropriate rating of the motor.
Important: In order to avoid nuisance trips, the
overload setpoint dial must be adjusted to
the following calculated value:
Overload Setting = (Motor FLA)
Overload Setting = (Compressor RLA) x 1.12
Return Plenum Pressure High Limit
The Return Plenum Pressure High Limit Setpoint has a
non-adjustable value of 3.5 iwc. When the return plenum
pressure exceeds the Return Plenum Pressure High Limit
for more than 1 second, a "Return Pressure shutdown"
signal is sent, and an automatically resetting diagnostic is
set. After the return fan is off, the Return Pressure
Shutdown signal is cancelled.The unit will not be allowed
to restart within 15 seconds of shutdown.Three
consecutive occurrences of the Return Plenum Pressure
exceeding the Return Plenum Pressure Limit will cause a
manual reset diagnostic.The occurrence counter will be
reset every time the unit goes through a reset, transitions
from Stop to Auto, or transitions into and out of Occupied
or Unoccupied control.
Low Pressure Control (LPC)
LPC is accomplished using a binary input device. LP
cutouts are located on the suction lines near the scroll
compressors.The LPC contacts are designed to close
when the suction pressure exceeds 41± 4 psig. If the LP
control is open when a compressor is requested to start,
none of the compressors on that circuit will be allowed to
operate.They are locked out and a manual reset diagnostic
is initiated.
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The LP cutouts are designed to open if the suction
pressure approaches 25± 4 psig. If the LP cutout opens
after a compressor has started, all compressors operating
on that circuit will be turned off immediately and will
remain off for a minimum of three minutes. If the LP cutout
trips four consecutive times during the first three minutes
of operation, the compressors on that circuit will be locked
out and a manual reset diagnostic is initiated.
Saturated Condenser Temperature Sensors
(2RT1 and 2RT2)
These analog input devices are mounted inside a
temperature well located on a condenser tube bend.They
monitor the saturated refrigerant temperature inside the
condenser coil and are connected to the SCM/MCM
(1U49). As the saturated refrigerant temperature varies
due to operating conditions, the condenser fans are cycled
"On" or "Off" as required to maintain acceptable
operating pressures. For evaporative condensers, this
value is determined by the MPM which converts a pressure
to a temperature value that is sent to the MCM to be used
for head pressure control.
Head Pressure Control (HPC)
This is accomplished using one saturated refrigerant
temperature sensors per refrigeration circuit. During a
request for compressor operation, when the condensing
temperature rises above the "lower limit" of the control
band, the Compressor Module (SCM/MCM) starts
sequencing condenser fans "On" . If the operating fans can
not bring the condensing temperature to within the
control band, more fans are turned on.
As the saturated condensing temperature approaches the
lower limit of the control band, fans are sequenced "Off" .
The minimum "On/Off" time for condenser fan staging is
5.2 seconds. If the system is operating at a given fan stage
below 100% for 30 minutes and the saturated condensing
temperature is above the "efficiency check point" setting,
a fan stage will be added. If the saturated condensing
temperature falls below the "efficiency check point"
setting, the fan control will remain at the present operating
stage. If a fan stage cycles four times within a 10 minute
period, the control switches from controlling to the "lower
limit" to a temperature equal to the "lower limit" minus
the "temporary low limit suppression" setting. It will
utilize this new "low limit" temperature for one hour to
reduce condenser fan short cycling.
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 control the sump pump.
When the temperature rises above the Upper Limit (120F)
the Sump Pump is energized. If the Condensing
Temperature drops below the Lower Limit (70F) the Sump
Pump is de-energized.
RT-SVX36K-EN