Trane CAUC-C20, Installation Operation & Maintenance, Page: 29 / 44

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System Start-Up
Sequence of Operation
Standard Model 20 through 60 Ton air cooled condensers
function as the outdoor condensing units for appropriately
sized split refrigeration systems. These units, operating in
conjunction with a matched indoor compressor/evaporator
configuration, provide refrigerant condensing for these sys-
tems down to a normal ambient temperature of 40 F. Opera-
tion to 0
o F ambient is possible with the addition of externally
mounted low ambient dampers.
All condenser fans are direct drive, 26 inch propeller type.
They are driven by 1 HP thermally protected motors.
Condenser fan cycling is accomplished through interlocking
the fan operation with compressor operation (5K1 & 5K2),
liquid line pressure switches (4S11 & 4S12). When the low
ambient option is applied, ambient temperature thermostats
(1S36 & 1S37) are used to provide additional fan cycling
control. Table 5-1 lists the condenser fan sequencing data
and Figure 5-1 illustrates the condenser fan locations with
their respective fan and relay designators.
When wired properly, the unit will start and operate satisfac-
torily as long as the operating temperature is above the
minimum operating temperature listed in Table 5-2.
The condensing unit operation starts and stops automati-
cally when the cooling demand is initiated and terminated
by the cooling circuit interlock relays illustrated in
Figure 5-2.
The control components are mounted in the various areas
of the unit as illustrated in Figure 5-3.
Table 5-1
Condenser Fan Sequencing Data
Controlling Fan Fan Fan
Device (3) "ON" "OFF" Identification
Customer
Interlock 5K1 5K1 2B1, 2B2, 2B3 (1)
Circuit 1 Closed Open
Customer
Interlock 5K2 5K2 2B4, 2B5, 2B6 (1)
Circuit 2 Closed Open
Fan
1S36 (2)
Temperature 67.5
o
F 65 F 2B3 (1)
Switch
1S37 (2)
67.5
o
F 65 F 2B6
Fan
4S11
Pressure
275 psig 155 psig 2B1 (1)
Switch
4S12
275 psig 155 psig 2B6
Notes:
1. Bold fan identifies fans used on 25, 30, 50 & 60 Ton
units only.
2. 1S36 and 1S37 normally-closed contacts open on
ambient temperature drop to 65
o
F. Contacts reclose
on ambient temperature rise to 67.5
o
F.
3. Above data does not apply when units are interfaced
with Trane Model CCAD package chillers. UCM for
the CCAD unit commands fan control.
Low Ambient Damper Operation
Low Ambient Dampers are available as a factory installed
option or can be field-installed. Dampers are used to extend
the operation of these units from the standard operational
temperatures to a minimum of 0
o F without hot gas bypass
or 10 o F with hot gas bypass. (These values apply when
wind speed across the condenser coil is less than 5 m.p.h.).
If typical wind speeds are higher than 5 m.p.h., a wind
screen around the unit may be required. By restricting the
airflow across the condenser coils, saturated condensing
temperatures can be maintained as the ambient tempera-
tures change.
The low ambient damper actuator controls damper modula-
tion for each refrigerant circuit in response to saturated con-
densing temperature.
Low Ambient Thermostat Operation
In addition to the low ambient dampers on 25, 30, 50 & 60
Ton units, a low ambient thermostat is installed to further re-
strict the airflow across the condenser by cycling the 2B3
condenser fan on 25 & 30 Ton units plus 2B6 on 50 & 60
Ton units. The thermostat opens when the ambient tem-
perature approaches 65
o
F and closes at approximately
67.5 o F.