TK 61552-2-MM-EN
29
•
Null
•
Modulated Heat (Continuous operation only)
•
Hot Gas Heat
•
Full Heat
•
Defrost
N
No
otte
ess::
1. ETV Operation and Null mode ONLY if controller setpoint is below Fresh/Frozen
temperature setting
2.
ETV operation is locked out during CYCLE-SENTRY operation.
3. Null mode if setpoint is below Fresh/Frozen temperature setting.
4. During Cycle Sentry Operation:
•
After initial unit start-up and unit pull-down to setpoint, the controller limits Low
Speed Cool operation when the controller setpoint is below Fresh/Frozen
temperature setting. On increasing compartment temperature, the unit operates in
Low Speed Cool for a maximum of 8 minutes in an attempt to reach setpoint. If
setpoint is not reached within 8 minutes, the unit will operate in High Speed Cool
until setpoint is reached
•
Unit mode is Null when the engine temperature and battery are satisfied.
Defrost
Frost gradually builds-up on evaporator coils as a result of normal operation. The unit uses hot
refrigerant to defrost the evaporator coils. Hot refrigerant gas passes through the evaporator coil
and melts the frost. The water flows through collection drain tubes onto the ground. The
methods of Defrost initiation are Automatic and Manual.
A
Au
utto
om
ma
attiicc D
De
effrro
osstt:: The controller is programmed to automatically initiate timed or demand
defrost cycles. The controller can be programmed to initiate timed defrost cycles at intervals of 2,
4, 6, 8, or 12 hours. Demand defrost cycles occur if the differences between the return air
temperature, discharge air temperature, and coil temperature exceed certain limits. The unit can
enter defrost cycles as often as every 30 minutes if required.
M
Ma
an
nu
ua
all D
De
effrro
osstt:: In Manual Defrost Mode, the operator initiates a defrost cycle. See “Initiating a
Manual Defrost Cycle”.
N
No
otte
e:: The unit will not perform a Manual Defrost cycle unless the unit has been turned on with
the ON key, the unit is running in Continuous or CYCLE-SENTRY mode (or shut down in
CYCLE-SENTRY Null mode), and the coil temperature is below 45 F (7 C).
The evaporator coil temperature must be below 45 F (7 C) to allow defrost.
The following four defrost timers are used. These timers can be set for intervals of 2, 4, 6, 8 or 12
hours.
•
Defrost Interval In Range with Fresh Setpoint (standard setting 6 hours)
•
Defrost Interval Not In Range with Fresh Setpoint (standard setting 4 hours)
•
Defrost Interval In Range with Frozen Setpoint (standard setting 6 hours)
•
Defrost Interval Not In Range with Frozen Setpoint (standard setting is 4 hours)
This feature allows a shorter Defrost interval to be used when the unit is out of range during a
pull-down 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 initiated on demand.
Use a shorter defrost interval if defrost is frequently being initiated on demand.
If the unit is in CYCLE-SENTRY Null mode, the engine will start when defrost is initiated. The unit
will stay in defrost until the evaporator coil temperature rises to 58 F (14 C).
