Thermo King SB-190 30, Manual

Page: 22 / 119

Unit Description (Rev. 12/03)
12
Diesel Operation
In diesel operation the microprocessor will select the oper-
ating mode from the list of possible modes below:
• High Speed Cool
• Low Speed Cool
• Low Speed Modulated Cool (optional ETV only)
• Null (CYCLE-SENTRY operation only)
• Low Speed Modulated Heat (optional ETV only)
• Low Speed Heat
• High Speed Heat
• Defrost
Defrost
Defrost is initiated manually through the defrost prompt
screen using the microprocessor Mode key and Enter key.
Defrost is initiated automatically on demand by the micro-
processor or by a defrost timer.
The evaporator coil temperature must be below 45 F (7 C)
to allow defrost. When the Defrost Icon appears, the damper
door is closed by the damper solenoid.
A demand defrost cycle will occur in the following two
instances:
If the differences between the return air temperature, dis-
charge air temperature, and coil temperature are greater than
predetermined values.
Two defrost timers are used. When the unit is In-Range
(within a few degrees of setpoint), defrost intervals are con-
trolled by the Defrost Interval In-Range timer (DEFI). This
timer can be set for 4, 6, 8 or 12 hours. The standard setting
is 6 hours. When the unit is not In-Range, defrost intervals
are determined by the Defrost Interval Not In-Range timer
(DEFN). This timer can be set for 2, 4, 6, 8 or 12 hours. The
standard setting is 4 hours. This feature allows a shorter
defrost interval to be used when the unit is out of range dur-
ing a pulldown and more frequent defrost cycles may be
beneficial.
Normally, longer defrost timer intervals are used for colder
loads. The defrost interval may need to be changed if the
unit will not hold the compartment temperature at setpoint.
• Use a longer defrost interval if defrost is not being initi-
ated on demand.
• Use a shorter defrost interval if defrost is frequently
being initiated on demand.
Data logger event codes starting with the letters DFF, DFI,
and DFT are logged when defrost occurs on units equipped
with data logging. DFF indicates defrost was forced. DFI
indicates defrost was initiated manually. DFT indicates
defrost was initiated by a timer.
If the unit is in CYCLE-SENTRY Null mode, the engine
will start when defrost is initiated. The In-Range Icon will
remain on if it was on when defrost was initiated.
The unit will stay in defrost until the evaporator coil tem-
perature rises to 58 F (14 C). If the evaporator coil tempera-
ture does not rise above 58 F (14 C) within the Defrost
Duration (DDUR) time limit, the microprocessor will termi-
nate defrost. The Defrost Duration can be set for either 30 or
45 minutes.