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O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
High Pressure Cutout Switch (HPC)
Each VS and FS compressor has an HPC installed in its
discharge line. The switch is set to open at 553 psi +/-
15 and re-close at 424 +/-30.
I I m m p p o o r r t t a a n n t t : : The HPC is wired into each compressors
Enable circuit, and the VS and FS
compressor enable circuit are unique. The
FS compressor enable circuit uses 24 Vac
power sourced from the Control Power
Transformer, where the VS compressor
enable circuit uses 24 Vdc power sourced
from the VS compressor drive.
Inadvertently applying 24 Vac to the VS
drive terminal block will permanently
damage the drive.
On the fixed speed compressors, if an HPC opens, the
24 Vac power that energizes the compressor start
contactor is interrupted and the compressor will turn
off. The Unit Controller will detect this and lock the
circuit out on a High Pressure Cutout.
On the variable speed compressor, a 24 Vdc signal
originates from terminal #22 on the 1U1 and is routed
through the NC contact of the VS compressor HPC.
That signals return must be sensed on terminal #31 of
the 1U1. If that signal is lost due to an HPC or
Emergency Stop input, the compressor will
immediately shut down. The Unit Controller will detect
HPC trip and lock the circuit out on a High Pressure
Cutout.
Compressor Input/Output Module
Each compressor has a dedicated XM30 input/output
module that communicates digitally with the Unit
Controller (XM30.8, 9, 10, and 11 for compressors A, B,
C, and D, respectively). The XM30 module is used to
sense its respective suction and discharge pressure
sensor, suction temperature sensor, and control the
condenser water regulating valve via a 0-10 Vdc output.
Compressor Pressure Sensors
Each compressor has its own set of suction and
discharge pressure sensors. The sensors are powered
by the 5 Vdc power supply 2U1. Their range is 0-600
psig and their voltage output is linearly proportional to
the sensed pressure.
The discharge pressure sensor is used by the Unit
Controller to do the following:
•
control the optional WRV (if equipped)
•
compute compressor differential pressure
•
warn the user if a high discharge pressure condition
occurs
•
activate the VS compressor Limit Condition control
function
The suction pressure sensor is used by the Unit
Controller to do the following:
50
•
detect low suction pressures
•
compute compressor suction superheat
•
compute compressor differential pressure
•
activate the VS compressor Limit Condition control
function
Compressor Suction Temperature
Each compressor has its own suction temperature
thermistor. It is used to compute compressor suction
superheat. If superheat is less than 4 degrees for 5
minutes, or more than 25 degrees for 10 minutes, the
circuit is locked out on a fault and a diagnostic is
annunciated.
Fixed Speed Compressor (FS)
Each FS compressor has two 24 Vac, 30W crankcase
heaters. The power for these heaters is routed through
a NC auxiliary contact on it's respective start contactor.
This way the heater is energized whenever the
compressor is Off.
In each FS compressor motor junction box is a 24 Vac
powered CoreSense™ compressor protection module
(MCSP). This module displays compressor status and
diagnostics and provides the following protections:
•
motor temperature protection
•
missing phase protection
•
reverse phase protection
•
low control circuit voltage protection
•
short cycling detection and alert
If the CoreSense™ module detects a fault condition it
opens a dry contact on the module interrupting power
to that compressors run contactor coil. The power
interruption is detected by the Unit Controller, which
disables the compressor and annunciates a
Compressor Safety Circuit diagnostic. After the cause
of the fault is remedied, a latching fault can be cleared
by cycling 24 Vac module power.
Compressor Safety Circuit
Each fixed speed compressor has a Compressor Safety
Circuit intended to protect the circuit from a variety of
fault conditions and to distinguish those failures from
HPC trips.
For each FS compressor, 24 Vac power is routed in
order from the control power transformer (CPT)
through its respective:
1. HPC
2. MCSP dry contact
3. Circuit breaker auxiliary-1CB1, 1CB2, or 1CB3
4. Start/Stop NO contact on the XM32 binary output
module
5. Compressor start contactor coil-1K1, 1K2 or 1K3
PKG-SVX027C-EN
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