Carrier 69NT40-541-505, Operation And Service Manual, Page: 85 / 143

5–5 T-368
(0.9°F) or greater between the supply air sensors and/
or a difference of 2.0°C (3.6°F) between the return air
sensors. Probe disagreement found in either pair can
trigger a defrost probe check.
In Frozen Mode, only the controlling probes are consid-
ered. Disagreement of the controlling probes can trig-
ger a defrost probe check, which will occur when the
difference between the sensors is greater than 2.0°C
(3.6°F). Normally, the controlling probes are the return
probes but if both return probes are invalidated, the
supply probes are used for control purposes. Probe
disagreement of the non
− controlling probe pair will not
trigger a defrost probe check.
If, after the defrost probe check, the supply probes
agree and return probes agree, all supply and return
sensors are considered valid and the unit returns to
normal control.
In the Case of Probe Disagreement:
If the supply probes disagree and the return probes
agree, the controller will invalidate the worst supply
probe. If the probe check is run as part of Pre
− trip P − 5,
an alarm will be triggered for the invalidated probe. If it
is a run time defrost probe check, the invalidated probe
will be passed over and no alarm will be triggered.
However, if the best supply probe is greater than 1.2°C
(2.2°F) difference with respect to its return probes, the
best supply probe is also invalidated. If unit is in Perish-
able Mode, a probe alarm will be triggered for both sup-
ply probes.
If the supply probes agree and the return probes dis-
agree, invalidate the worst return probe. If the probe
check is being run as part of Pre
− trip P − 5, an alarm will
be triggered for the invalidated probe. If it is a run time
defrost probe check, the invalidated probe will be
passed over and no alarm will be necessary. If the best
return probe is greater than 1.2°C (2.2°F) difference
with respect to its supply probes, then the best return
probe is also invalidated. If the unit is in perishable
mode, a probe alarm will be triggered for both return
probes.
5.9 EMERGENCY BYPASS OPERATION
(OPTION)
Operation by the refrigeration controller may be over-
ridden by use of the EMERGENCY BYPASS switch.
The EMERGENCY BYPASS switch functions to
bypass the controller in the event of controller failure.
To place the unit in the emergency bypass mode, cut
the wire tie installed at the switch mounting and place
the EMERGENCY BYPASS switch in the BYPASS
position. This will in turn activate the Emergency
Bypass System (EBS) control module.
To operate the fans only, the MODE switch must be in
the FANS ONLY position and the EMERGENCY
BYPASS Switch must be in the ON position.
The EBS module uses the system safety devices (high
pressure switch, motor internal protectors, and heat
termination thermostat) to protect the system while in
Emergency Bypass Mode.
CAUTION
!
The unit will remain in the full cooling mode
as long as the emergency bypass switch is
in the BYPASS position and the MODE
SWITCH is in the FULL COOL position.
If the cargo is at risk of being damaged
by low temperatures, the operator must
monitor container temperature and man-
ually cycle operation as required to main-
tain temperature within required limits.
In the ON position the EBS will be enabled. With the
MODE SWITCH in the FULL COOL MODE. The follow-
ing will occur simultaneously:
1. The EBS switch will enable EBS input.
2. The phase detection circuit will detect the phase
rotation and close to provide power to the com-
pressor contactor.
3. The condenser fan contact will close to energize
the condenser contactor and provide power to
the condenser fan motor.
4. The evaporator fan contact will close to energize
the high speed evaporator contactor and pro-
vide power to the evaporator fan motor.
5. The EBS electronic module will open the SMV to
100%.
To return the unit to normal operation, place the EBS
switch in the NORMAL OPERATION position. When
emergency operation is no longer required, re-install
the wire tie at the switch mounting.
Downloaded from ManualsNet.com search engine