Defrost Related Settings; Protection Modes Of Operation; Evaporator Fan Operation; Failure Action - Carrier 69NT40-541-505 Operation And Service Manual

The SMV is independently operated by
the microprocessor. Complete schemat-
ics and legends are located in
8.1.
Defrost will terminate when the DTS reading rises
above one of two model number configurable options
selection, either an upper setting of 25.6°C (78°F)
which is default or lower setting of 18°C (64°F).
When the DTS reading rises to the configured setting,
the de-icing operation is terminated
4.3.19

Defrost Related Settings

DTS Failure
When the return air temperature falls to 7°C (45°F), the
controller ensures that the defrost temperature sensor
(DTS) reading has dropped to 10°C or below. If it has
not it indicates a failed DTS, a DTS failure alarm is trig-
gered and the defrost mode is operated by the return
temperature sensor (RTS). Defrost will terminate after
1 hour.
If the DTS fails to reach is termination setting, the
defrost terminate after 2 hours of operation.
Defrost Timer
If CnF23 is configured to "SAv" (save), then the value
of the defrost interval timer will be saved at power
down and restored at power up. This option prevents
short power interruptions from resetting an almost
expired defrost interval, and possibly delaying a
needed defrost cycle. If the save option is not selected
the defrost timer will re-initiate and begin recounting.
If CnF11 is model number configured to OFF the oper-
ator will be allowed to choose "OFF" as a defrost inter-
val option.
If CnF64 is configured in the operator will be allowed to
choose "PuLS" as a defrost interval option. For units
operating with "PuLS" selected, defrost interval is
determined by the unit temperature setpoint and the
Evaporator Fan Pulsing Temperature Setting (Cd60).
When the unit temperature setpoint is equal to or less
than the Evaporator Fan Pulsing Temperature Setting,
the defrost interval is set to 6 hours. Otherwise, the
defrost interval is determined using the Automatic
Defrost Interval Determination logic. In either case,
"PuLS" remains displayed in this function select code.
If any Auto Pretrip sequence is initiated, Cd27 will be
set to 'AUTO' unless CnF49 (OEM Reset) is set to
"Custom" AND CnF64 (Evaporator Fan Pulsing Logic)
configuration variable is set to IN, in which case Cd27
will be set to "PuLS".
If defrost does not terminate correctly and temperature
reaches the set point of the Heat Termination Thermo-
stat (HTT) 54°C (130°F), the HTT will open to de-ener-
gize the heaters (AL59 & AL60). If the HTT does not
open and termination does not occur within two hours,
the controller will terminate defrost. AL60 will be acti-
vated to inform of a possible DTS failure.
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4.4

PROTECTION MODES OF OPERATION

4.4.1
Opening of an evaporator fan internal protector will
shut down a unit. (CnF32 set to 2EFO).
Section
4.4.2
Function code Cd29, Failure Action Mode, may be opera-
tor set to allow continued operation in the event the con-
trol sensors are reading out of range. The factory default
is full system shutdown (refer to
4.4.3
Function codes Cd31, Stagger Start Offset Time, and
Cd32, System Current Limit, may be operator set to con-
trol start-up sequence of multiple units and operating cur-
rent draw. The factory default allows on demand starting
of units and full current draw (refer to
4.4.4
When configuration variable CnF14 is set to "In," the
condenser pressure control logic is activated to maintain
discharge pressures above 130psig in low temperature
ambients. The logic turns the condenser fan on or off in
accordance with the condenser pressure transducer
reading (refer to
when the following conditions are met:
1. The ambient sensor reading is less than or
equal to 27°C (80°F), and
2. Voltage/Frequency ratio is less than or equal to
8.38.
When 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 saturated condensing pressure is greater
than 200psig OR if the condenser fan has been OFF
for a variable time period of up to 60 seconds depend-
ing on the ambient temperature. As the ambient tem-
perature increases, the amount of time that the
condenser fan is energized will correspondingly
increase towards the maximum.
If the condenser fan is ON, it will de-energize only if the
saturated condensing pressure is less than 130psig and
the condenser fan has been running for a minimum of
thirty seconds depending on the ambient temperature.
4.5 QUEST − CCPC
Compressor−Cycle Perishable Cooling (CCPC) is a
method of temperature control during steady−state per-
ishable cooling that cycles the compressor on and off
according to return air temperature.
To be eligible for steady−state control the unit must first
complete a "setpoint pulldown" phase and a "CCPC pull-
down" phase:
4–11

Evaporator Fan Operation

Failure Action

Table

Generator Protection

Condenser Pressure Control

Table 4–4) The function is enabled
4–5).
Table 4–5).
T-368