Carrier 69NT40-561-201, Operation & Service Manual, Page: 40 / 117

3 − 11 T-364
3.3.21 Defrost Related Settings
The probe check is a test that compares temperature
sensor readings to determine if any sensors have failed.
If probe check fails, the system will run for eight minutes
to validate. At the end of eight minutes, probe alarms will
be set or cleared based on the current conditions.
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 (50 F) or below. If it
has not it indicates a failed DTS, a DTS failure alarm is
triggered and the defrost mode is operated by the return
temperature sensor (RTS).
The value of the defrost interval timer will be saved at
power down and restored at power up. This option pre-
vents short power interruptions from resetting an almost
expired defrost interval, and possibly delaying a needed
defrost cycle.
After a new Defrost Interval is selected, the previously
selected Interval is used until the next defrost termina-
tion, the next time the DTT contacts are OPEN, or the
next time power to the control is interrupted.
If any Auto Pretrip sequence is initiated, Cd27 will be set
to ’AUTO’.
3.4 PROTECTION MODES OF OPERATION
3.4.1 Evaporator Fan Operation
Opening of an evaporator fan internal protector will shut
down the unit.
3.4.2 Failure Action
Function code Cd29 may be operator set to select the
action the controller will take upon a system failure. The
factory default is full system shutdown. Refer to
Table 3 − 5.
3.4.3 Generator Protection
Function codes Cd31(Stagger Start, Offset Time) and
Cd32 (Current Limit) may be operator set to control the
start up sequence of multiple units and operating current
draw. The factory default allows on demand starting (no
delay) of units and normal current draw. Refer to
Table 3 − 5.
3.4.4 Compressor High Temperature Protection
The controller continuously monitors compressor dis-
charge pressure and temperature, and suction pres-
sure. If discharge pressure or temperature rises above
the allowed limit or suction pressure falls below the al-
lowed limit, the compressor will be cycled off and on
every 3 minutes. Condenser and evaporator fans will
continue to operate during the compressor off cycle.
If high compressor dome temperature occurs, as meas-
ured by the compressor discharge temperature sensor
(CPDS), the controller will allow additional refrigerant to
be released into the system in order to provide cooling to
the evaporator coil and compressor dome. The control-
ler is alerted to high compressor dome temperatures via
the CPDS when ambient temperature is greater than
43.3 C (110 F), return air temperature is less than
-17.5 C (.5 F) and the compressor discharge temper-
ature is greater than 117.7 C (244 F).
Dome temperature control logic will disengage when re-
turn air temperature and ambient temperature return to
allowed limits or when the compressor turns off.
3.4.5 Compressor Low Pressure Protection
If the suction pressure low limit is triggered, the DUV will
energize to raise the suction pressure.
3.4.6 Perishable Mode - System Pressure
Regulation
In perishable mode, system pressures may need to be
regulated at ambient temperatures of 20 C (68 F) and
below. Once below this ambient temperature, the con-
denser fan may cycle on and off based on limits imposed
for discharge pressure. For extremely cold ambient
temperatures, -18 C (0 F), heater cycling may occur
within normal system operation based on discharge
pressure limits.
3.5 CONTROLLER ALARMS
Alarm display is an independent controller software
function. If an operating parameter is outside of ex-
pected range or a component does not return the cor-
rect signals back to the controller, an alarm is gener-
ated. A listing of the alarms is provided in Table 3 − 6.
The alarm philosophy balances the protection of the re-
frigeration unit and that of the refrigerated cargo. The
action taken when an error is detected always considers
the survival of the cargo. Rechecks are made to confirm
that an error actually exists.
Some alarms requiring compressor shutdown have
time delays before and after to try to keep the compres-
sor on line. An example is alarm code “LO,” (low main
voltage), when a voltage drop of over 25% occurs, an in-
dication is given on the display, but the unit will continue
to run.
When an Alarm Occurs:
a. The red alarm light will illuminate for alarm code num-
bers 15, 17, 20, 21, 22, 23, 24, 25, 26, and 27.
b. If a detectable problem exists, its alarm code will be
alternately displayed with the set point on the left
display.
c. The user should scroll through the alarm list to deter-
mine what alarms exist or have existed. Alarms must
be diagnosed and corrected before the Alarm List can
be cleared.
To Display Alarm Codes:
a. While in the Default Display mode, press the ALARM
LIST key. This accesses the Alarm List Display Mode,
which displays any alarms archived in the alarm
queue.
b. The alarm queue stores up to 16 alarms in the se-
quence in which they occurred. The user may scroll
through the list by depressing an ARROW key.
c. The left display will show “AL##,” where ## is the
alarm number sequentially in the queue.
d. The right display will show the actual alarm code.
“AA##” will display for an active alarm, where “##” is
the alarm code. Or “IA##” will display for an inactive
alarm, see Table 3 − 6.
e. “END” is displayed to indicate the end of the alarm list
if any alarms are active.