4–27
T-362
Figure 4.8 Defrost
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
Defrost Temperature Sensor (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.
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 operator will be allowed to choose “OFF” as a defrost interval
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 set point and the Evap Fan
Pulsing Temp setting
on the Trip Settings screen. When the unit temperature set point 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, the Defrost Interval setting 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 the Defrost Interval setting on the Trip Settings screen will be set to “Pulse”.
If defrost does not terminate correctly and temperature reaches the set point of the Heat Termination Thermostat
(HTT) 54°C (130°F), the HTT will open to de-energize the heaters (AL059 & AL060). If the HTT does not open and
termination does not occur within two hours, the controller will terminate defrost. AL060 will be activated to inform
of a possible DTS failure.
24 VOLT POWER
ENERGIZED
DE-ENERGIZED
TN
ST
F
HPS
PB
IP-CM
TC
CF
TE
IP-EM1
EF
IP-EM2
HTT
TH
HR
ESV
TS
TV
EF
ES
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