Trane IntelliPak SCWG 020, SCWG 025, SCWG 030, SCWG 035, SWG 020, SWG 025, SWG 030, SWG 035, SCRG 020, SCRG 025, SCRG 032, SRG 020, SC Installation Manual page 96

96
Owner
Compressor Safety Devices
The compressors have motor
temperature cutout switches in the motor
windings. These switches are provided to
take the compressors off line during high
motor winding temperature conditions.
If a compressor low pressure cutout
opens during compressor start-up, the
UCM will not shut the compressor off
during the first two to three minutes after
start-up. This prevents possible nuisance
trips during low ambient start conditions.
See Table O-SO-2.
Each compressor's discharge line
contains a high pressure cutout. Under
abnormal operating conditions, the cutout
will open to stop compressor operation.
Table O-SO-2. Pressure Cutouts.
Unit High Pressure
Model Cutout
SXWG 360/270
SXRG 425/350
Step Control
Steps of mechanical cooling are control
based on supply air or zone temperature.
See Table O-SO-1 on page 95 for
compressor staging.
Capacity is based on an integrating
control concept. The unit capacity
matches the existing load and maintains
an average supply air temperature within
the supply air setpoint temperature
Table O-SO-3. IntelliPak
Unit Tons
SCWG 20
SCWG 25
SCWG 30
SCWG 35
Table O-SO-4. Thermostat Controlled Unit Cooling Capacity
Stages.
Unit
Size
% Capacity Utilized
SCWG 20
SCWG 24
SCWG 30
SCWG 35
SCRG 20
SCRG 25
SCRG 32
Sequence of
Operation
control band region.
The supply air temperature control band
is centered around supply air tempera-
ture setpoint and is adjustable from 2 to
12 F . In a steady state, the unit will either
maintain a constant level of cooling
capacity with the supply air temperature
within the control band, or the highest
active cooling level will cycle to provide
an average supply air temperature equal
to the setpoint.
If the supply air temperature swings
outside the limits of the control band, the
mechanical cooling capacity will increase
or decrease by one level accordingly. The
change occurs by integrating the tem-
perature offset from the control band
limit.
A minimum time delay of five minutes
follows each change in cooling level. This
Low Pressure
Cutout
time delay promotes stability by allowing
20/35
the system to respond to the change
12/27
before any further control action occurs.
As the supply air temperature ap-
proaches setpoint, the time duration
between changing levels of cooling
capacity increases.
See Figure O-SO-2 for the typical unit
operating curve. Figure O-SO-3 shows
typical unit performance when supply air
temperature swings exceed the control
band limits.
Adjust the supply air temperature control
® Unit Cooling Capacity Percent.
Cooling Stage % Utilized
Cool 1 Cool 2
53 100
53 100
47 65
53 100
Cooling Stages
Cool 1 Cool 2
% Capacity Utilized
53 100
53 100
65 100
53 100
52 100
47 100
52 100
Cool 3
n/a
n/a
100
n/a
SCXG-SVX01B-EN