Electrical Control & Protection System - Trane CGA-SVX01A-EN Installation, Operation And Maintenance Manual

ELECTRICAL CONTROL &
PROTECTION SYSTEM
Low Pressure Cutouts (LP1, LP2)
These units are protected by low pressure
cutouts that open and stop compressor
operation if the operating pressure drops
below 45 ± 4 psig . The cutout automatically
resets when the pressure reaches 60 ± 4
psig. The LP is a SPDT device and if it
opens at low ambient start-up, there will be
a 1.5 minute override to prevent nuisance
trip-outs ( for LAU only).
For CGAR unit, the low pressure cutout
setpoints 25 ± 4 psig.
High Pressure Cutouts (HP1, HP2)
These units have high pressure cutouts that
open and stop compressor operation if the
discharge pressure reaches 405 ± 7 psig.
The cutout automatically resets when
pressure drops to 300 ± 20 psig.
Reset Relays (CR1,CR2)
If the unit is shut down by safety devices
(LP, HP, FS, FU, KF etc.) the reset relay
locks out the compressor contactor (MC1,
MC2). This prevents the system from
recycling until the condition that caused the
safety devices to trip is determined and
corrected.
CAUTION: To prevent unit damage, do
not reset the control circuit until the
cause of the safety lockout is identified
and corrected.
To reset CR1 and CR2, open and reclose
the unit REMOTE/OFF/ON switch.
Anti-freeze Cutout (FS1, FS2, FU)
The FS and FU are designed to protect the
evaporator from freeze damage in the event
of a water temperature thermostat (WTT)
malfunction or restricted water flow. The
© American Standard Inc. 2001
FU's remote sensing bulb is mounted at the
outlet end of the evaporator, where it
monitors leaving water temperature. If
during normal unit operation, the leaving
chilled water temperature falls to the trip
point, the FU will open to interrupt compres-
sor operation.
When leaving chilled water temperature falls
down, the suction temperature also falls
down. For further protection to avoid freeze
damage, another freezestat ( FS1 , FS2 ) in
contact with the suction line. If suction
temperature falls to the trip point , the FS1
(FS2) will open to interrupt compressor
operation.
Motor Overloads
These units have internal compressor and
condenser fan motor overloads to protect
the motors from overcurrent and overheat-
ing conditions and automatically reset as
soon as they cool sufficiently. Pump motor
has thermal overload installed at the load
contactor. Pump overload needs manual
reset.
Cooling Mode
Water Temperature Thermostat
Operation (TS1, TS2) for cooling mode
For Double Refrigeration Circuit Operation
At Start-up, the pump will come on immedi-
ately. Two minutes after the pump is on and
EWT(entering water temperature)is above
14.0 °C, compressor
1 will start. One
minute later, if the EWT is above 13.5°C,
compressor 2 will start.
When cooling demand is met and EWT
drops to 10.0 °C. Compressor
1 will stop,if
EWT continues to fall to 9.5 °C,compressor
2 will stop. Subsequently,when load
builds up and EWT rises to 13.5 °C com-
pressor 2 comes on, and if EWT rises
further to 14.0°C, compressor 1 comes on.
24
Pump remains on unless the unit is turned
off.
For Single Refrigeration Circuit Operation
For units with only one refrigerant circuit, the
operation of water pump, fan and compres-
sor is exactly the same. The only difference
is the unit will operate the single compressor
from any temperature over 14.0 °C and
10.0°C when the compressor will stop.
Heating Mode
Water Temperature Thermostat
Operation (TS3, TS4) for cooling mode
For Double Refrigeration Circuit Operation
At start-up, pump will come on immediately.
Two minutes after the pump is on and EWT
(entering water temperature)is below
38.0°C, compressor 1 will start. One
minute later, if EWT is below 39.0 °C,
compressor 2 will start.
When heating demand is met and EWT
rises to 42.0 °C, compressor
1 will stop, if
EWT continues to rise to 43.0
°C,compressor
2 will stop.
Subsequently,when load builds up and EWT
drops to 39.0 °C, compressor
2 comes on,
and if EWT drops further to 38.0 °C,
compressor 1 comes on. Pump remains
on unless the unit is turned off.
For Single Refrigeration Circuit Operation
For units with only one refrigerant circuit, the
operation of water pump, fan and compres-
sor is exactly the same. The only difference
is the unit will operate the single compressor
from any temperature below 38.0 °C and
42.0 °C when the compressor will stop.
CGA-SVX01A-EN