3-14
T-294-01
3.1.6
Condenser Pressure Control (CPC)
A pressure control system has been incorporated by
means of a condenser pressure transducer (CPT) and
condenser pressure control (CPC) logic to maintain
discharge pressures above 130 psig in low
temperatures.
In order for the CPC logic to be enabled, the following
conditions must be met:
S
CPC configuration variable set to “In”
S
CPT sensor is valid (alarm code AL68
inactive)
S
AMBS sensor is valid
(alarm code AL57 inactive)
S
AMBS is less than or equal to 26.6
_
C
(79.9
_
F)
S
Voltage/Frequency ratio is less than or equal
to 8.38
When condenser pressure control (CPC) is enabled (all
of the above conditions are met), either pressures or
timers may dictate a change of state from OFF to ON, or
ON to OFF. If the condenser fan is OFF, it will be
energized if saturation condensing pressure is greater
than 200 psig OR if the condenser fan has been OFF for
a maximum of sixty seconds depending on the ambient
temperature. If the condenser fan is ON, it will
de-energize only if the saturation condensing pressure is
less than 130 psig and the condenser fan has been
running for a minimum of thirty seconds depending on
the ambient temperature. As the ambient temperature
increases, the amount of time that the condenser fan is
energized will correspondingly increase.
If any one of the following conditions occur the CPC
logic will be disabled:
S
CPT sensor is invalid
(alarm code AL68 activates)
S
AMBS sensor is invalid
(alarm code AL57 activates)
S
AMBS is greater than 29.5
_
C (85.1
_
F)
S
Voltage/Frequency ratio is greater than 8.42
3.1.7
Controller Temperature Control
There are two control ranges, Frozen and Perishable
(chill). The Frozen range is active with set points
at or
below --10
_
C (+14
_
F), or --5
_
C (+23
_
F) optionally,
and the Perishable range is active at set points
above
--10
_
C (+14
_
F), or --5
_
C (+23
_
F) optionally. See
Figure 3-5 and Figure 3-6.
The Controller configuration variable for “Heat
Lockout” (refer to Table 3-1) can be changed for set
points of either --10
_
C (+14
_
F), or --5
_
C (+23
_
F)
optionally.
NOTES
S
When upward set point changes are made at
ambients below 27
_
C (80
_
F), the compressor
is immediately cycled OFF. The compressor
three minute time delay will be overridden, so
that as soon as the control temperature is at least
0.2
_
C (0.4
_
F) above set point the compressor
will turn ON.
S
At each manual power up of the unit, the
normally closed stepper motor SMV starts at a
6 to 21% open position, and the unit will run for
three minutes to boil off dissolved refrigerant
from the compressor oil, depending on ambient
conditions.
S
Depending on ambient conditions, the unit
may be in a pressure limiting mode which may
restrict the maximum SMV position.
S
Depending on the current limiting setting
and the environmental conditions, the SMV
position may be restricted.
3.1.7.1 Perishable (Chill) Range Above --10
_
_
_
_
C
(+14
_
_
_
_
F), or --5
_
_
_
_
C (+23
_
_
_
_
F) Optionally.
For set points
above
--10
_
C (+14
_
F), or --5
_
C (+23
_
F)
optionally, the Controller maintains SUPPLY air at the
set temperature by the following modes of operation:
a. Operation in the conventional mode without
dehumidification (Code 33 OFF)
1. At ambients below 27
_
C (80
_
F), the condenser fan
will cycle on/off depending on condenser pressure and
on/off times.
If the condenser pressure is greater than 200 psig OR the
condenser fan has been OFF at least 60 seconds, the
condenser fan will start.
If the condenser pressure is less than 130 psig AND the
condenser fan remains ON for at least 30 seconds, the
condenser fan will stop.
2. At ambients above 27
_
C (80
_
F), condenser
pressure control (CPC) is disabled and the condenser
fan runs continuously.
If the unit starts when ambient is below --10
_
_
_
_
C
(+14
_
_
_
_
F) and condenser pressure is below 200 psig,
the condenser fan will not start until pressure
reaches 200 psig.
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