CXRC-SVX01J-EN
21
Operating Principles
Control Sequences of Operation
for Units with IntelliPak
Typical Unit Operation
Sequence of operation will be described for a 60-ton
CCRC condenser attached to a 60-ton IntelliPak
controlled SCRF. All other configurations should be
discernible once the operator understands this
sequence.
When evaporator unit calls for mechanical cooling, the
compressor starts. The IntelliPak controller then starts
reading saturated condenser temperature sensor for
the circuit that started. Saturated condenser
temperature sensor probes are factory installed on the
condensing coils of the CCRC condensing unit.
When condenser temperature rises to a point that
condensing is required, the IntelliPak controller
initiates a call for condenser operation. Upon initial
start-up, the IntelliPak controller pulls in K1 and K2
relays simultaneously, thus pulling on all fans in circuit
1.
Condensing temperatures should then begin to fall as
condensing begins. As the temperature falls, the K1
relay drops out, thus dropping out circuit 1A fan 1 and
2 contactors and stopping circuit 1A fans 1 and 2. (The
IntelliPak controller will try to maintain a factory default
condensing temperature setpoint of 105°F.)
If saturated condenser temperatures continue to fall
with only circuit 1B fans 1 and 2 fans running, K2 relay
drops out and K1 relay re-engages. (See stages of fan
operation on CCRC schematics). K1 relay engages
circuit 1A fan 1 contactor, starting circuit 1A fan 1 only.
(Circuit 1B fan 1, 2 auxiliary contactor is no longer
engaged.)
If saturated temperature continues to drop with only
circuit 1A fan 1 running, the low ambient damper (if
equipped) begins to throttle the airflow to maintain
saturated condensing temperature. The SCRF actuates
the damper by way of a 2-10 VDC signal to the low
ambient damper actuator, thus maintaining head
pressure in a low ambient condition. The unit
continues to operate in this low ambient condition until
the cooling setpoint is satisfied, at which time, the unit
stops and halts all calls for condenser fan operation or
until the saturated condenser temperature begins to
rise.
If saturated condenser temperature begins to rise, low
ambient damper modulates open to allow more
airflow. If saturated condenser temperature continues
to rise with damper modulated fully open, K1 relay
drops out and the IntelliPak controller pulls in K2 relay,
subsequently pulling in contactor Circuit 1B fan 1, 2
auxiliary contactor. Upon closure of this contactor,
circuit 1B fans 1 and 2 start. (See stages of fan
operation on CCRC schematics).
There is no low ambient operation associated with
circuit 1B fans 1 and 2 operation. However the
saturated condenser temperature sensor continues to
monitor condensing temperature in order to make the
necessary adjustments to the fan operation. The
IntelliPak controller continually samples saturated
condenser temperature and stages up or down the fans
as required to maintain saturated condensing
temperature as read by the saturated condenser
temperature sensor probes (see stages of fan operation
on CCRC schematics).
If saturated condenser temperature continues to rise
with only K2 relay pulled in, the K1 relay re-engages
and again pulls in circuit 1A fan 1 contactor.
N
No
otte
e:: Circuit 1B fan 1, 2 auxiliary contactor is now
pulled in and will pull in circuit 1A fan 2
contactor, starting circuit 1A fan 2.
K1 and K2 relays are now simultaneously engaged thus
starting all fan operation in circuit 1. The unit stages
down in the reverse manner based on saturated
condensing temperature if and when saturated
condenser temperature begins to fall.
This is a detailed sequence of operation for the first
circuit to begin operation. If cooling load demands
require the second circuit to operate, the same
sequence of operation is valid and takes place
simultaneously utilizing IntelliPak controller relays K5
and K6.
Similar sequence of operation takes place on other
CCRC condensing unit sizes. Refer to the schematics,
including stages of fan operation, for specific unit
installed.
N
No
otte
e:: Low ambient dampers are optional. Not all units
may be equipped with low ambient dampers.
Low Ambient Damper Operation
Units with low ambient operation have two (2) low
ambient dampers. The dampers are used to extend
operation from standard low limit temperature to a
minimum of 0°F. Dampers modulate airflow across
condenser coils to maintain condensing pressure
during low ambient operation.
Optional low ambient (LA) dampers are controlled by
low ambient damper control module mounted in
control panel inside CCRC unit on a thermostat
controlled unit, or by the IntelliPak controller of SCRF
or SCRG.
