Defrost Related Settings; Figure 4.10 Defrost - Carrier PrimeLINE 69NT40-561-200 Operation And Service Manual

3. Probe Check: If defrost is initiated due to Probe Check immediately following the defrost cycle the evapora-
tion fans are started and run for eight minutes to stabilize the temperature throughout the container. A probe
check comparison is carried out at the end of the eight minute period if any sensor is found out of calibration.
At this time its alarm set is no longer used for control/reorder purposes.
4. Probe Check Logic: The logic determines that a Probe Check is necessary based on temperature values
currently reported by the supply and return probes
5. Delta T Logic: If the difference between return and supply air temperature (Delta T) becomes too great indi-
cating possible reduced airflow over the evaporator coil caused by ice buildup requiring a defrost.
a. In Perishable Pull Down - Delta T increases to greater than 12°C, and 90 minutes of compressor run
time have been recorded.
b. In Perishable Steady State – A baseline Delta T is recorded following the first defrost cycle after steady
state conditions are reached, (the unit is cooling, and the evaporator fans and heaters must remain in a
stable state for a period of five minutes). Defrost will be initiated if Delta T increases to greater than 4°C
above the baseline, and 90 minutes of compressor run time have been recorded.
c. In Frozen Mode - Defrost will be initiated if Delta T increases to greater than 16°C and 90 minutes of
compressor run time have been recorded.
When defrost is initiated, the controller closes the EEV, opens contacts TC, TN and TE (or TV) to de-energize the
compressor, condenser fan and evaporator fans.
The controller then closes contacts TH to supply power to the heaters. The orange DEFROST light and heat light
are illuminated and the COOL light is also de-energized.
The EEV and DUV are independently operated by the microprocessor. Complete schematics and legends are
located in Section 9.
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.
4.3.22

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 triggered
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.
T-362

Figure 4.10 Defrost

ENERGIZED
DE-ENERGIZED
F
HPS
IP-CM TN
IP-EM1 IP-EM2
HTT
ESV
TS
4–12
ST
24 VOLT POWER
TC PB
CF
TV
EF ES
TE EF
TH
HR