©2025 Copeland LP.
026-1803 R13 Supervisor I&O User Guide 9 - 54
Down times may only be used for hot gas and electric
type defrosts.
2. Defrost - During the defrost phase, refrigeration is
disabled. If using electric defrost heaters will be ON. If
using hot gas, heated refrigerant will be pumped through
the coil. This phase will continue until the defrost is
terminated.
3. Run-Off - After defrost heat is deactivated, the application
waits for the Run-Off time to pass before re-entering
refrigeration mode. This allows melted frost on the
evaporator to drain from the coil so that it will not re-
freeze when refrigeration begins again. After the user-
specified Run-Off time has passed, the defrost cycle has
ended. Run-Off times may only be programmed for hot
gas and electric type defrosts.
9.38.4.2 Defrost Types
There are many different ways used to defrost a refrigerated
case. A case controller is capable of using three different
types of defrost.
Off Cycle (Timed)
Off Cycle defrost (also known as Timed defrost) is simply a
period of time during which refrigeration is suspended. No
heat is applied to the evaporator. The application simply turns
refrigerant flow OFF for the duration of the defrost cycle.
When these defrost types are used, Pump Down and
Run-Off times are not necessary; therefore, they will not be
part of the defrost cycle.
Hot Gas and Reversed Cycle Hot Gas
Hot Gas and Reversed Cycle Hot Gas require the use of hot
gas from the refrigeration lines. During these types of defrost,
the application will open the valve and pump heated
refrigerant through the evaporator coil. Any user-defined
Pump Down and Run-Off times will be observed as normal.
Electric Defrost
Electric defrost uses electric heaters to defrost the evaporator
coil. During electric defrost, the application will turn the
Defrost output ON, which will likewise activate the heaters
connected to the power module’s defrost relay.
Any user-defined Pump Down and Run-Off times will be
observed as normal.
9.38.4.3 Defrost Termination
Both the start time and the end time of a defrost cycle are
determined by the user. The Pump Down, Defrost, and Run-
Off stages all have fixed durations, and when the last stage of
the cycle is complete, defrost is terminated.
However, a case controller may be programmed to terminate
the Defrost stage of the defrost cycle early if the temperature
inside the case rises above a fail-safe temperature setpoint.
For certain defrost types, defrost heat may also be “pulsed” in
order to keep the temperature below the setpoint without
terminating defrost.
Temperature Termination
One or more temperature sensors in the case circuit may be
designated as termination temperature sensors. The values
of these sensors are combined into a single control value,
and this value is compared to the setpoint. If the termination
control value is greater than the user-defined setpoint, defrost
will end, and the defrost cycle will begin the Run-Off period (if
applicable).
Termination sensors may be either analog temperature
sensors or digital closures (Klixons). Also, Case Circuit
applications may use the value of the analog case
temperature sensors for use in temperature termination.
Pulsed Defrost
Pulsed Defrost is only available if the circuit is using Electric or
Hot Gas defrost.
Pulsed Defrost is similar to Temperature Termination, except
when the termination temperature rises above the setpoint,
defrost does not terminate. Instead, the output that applies
defrost heat is turned OFF. The output will remain OFF until
the temperature falls below the setpoint, at which time the
output will come back ON.
The Case Circuit application will continue to pulse defrost in
this manner until the defrost time has passed. The defrost
cycle will then begin the Run-Off period.
9.38.4.4 Demand Defrost
If a case is configured with a demand defrost sensor, a case
controller may use their inputs as a means of keeping
scheduled defrost cycles from occurring when frost levels are
not high enough to require a defrost.
The optical demand defrost sensor may be either an analog
or digital type sensor. When this sensor detects no major
build-up of frost, the Case Circuit application ignores all
scheduled calls for defrost and continues in refrigeration
mode. When the sensor detects frost, the defrost inhibit is
canceled, and the case circuit will enter defrost at the next
scheduled time.
A demand defrost inhibit only keeps scheduled defrosts from
occurring. Any manual calls for a defrost cycle will occur as
normal. CCB demand defrost is currently not supported in the
Supervisory Controller. Demand sensors, if present on the
circuit, will be ignored.
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