Stop Of Defrost; Defrost Sequence - Danfoss AK-CC55 Compact User Manual

AK-CC55 Compact
Figure 16: Defrost start
Network:
The defrost start signal is received from a system manager via data communication.
Max. thermostat runtime:
When the aggregate time has passed a preset value, a defrost will be initiated.
Manual:
An extra defrost can be activated from the defrost button on the AK-UI55 Set display via the app, or via the
parameter setting. All the mentioned methods can be used in parallel – if just one of them is activated, a defrost will
be started.

Stop of defrost

Defrosting can be stopped by either:
• Time
• S4A temperature (with time as safety)
• S5A temperature (with time as safety)
When the selected defrost stop sensor reaches the set defrost stop limit, the defrost is terminated. If the defrost stop
sensor does not reach the set defrost stop limit within the set max. defrost time, the defrost will be terminated on
time.
Minimum defrost time
When using hot gas for defrosting, the heat is coming from within the evaporator, and this means that the S5 sensor
is rising fast when the inner layer of ice is melted. This will sometimes cause parts of the evaporator not to be
defrosted when defrost is terminated on S5 evaporator temperature.
To prevent this, the user is given the option of setting a minimum defrost time. When a defrost is initiated, it will
have to run for the set minimum time even if the set defrost stop limit has been reached by the selected defrost stop
sensor.

Defrost sequence

When a defrost is initiated, the controller will run through the following sequence:
1. Pump down: where the evaporator is emptied of refrigerant
2. Defrost: where the ice on the evaporator is melted
3. Hold after defrosting: where multiple controllers wait for each other (coordinated defrost)
4. Drip off: where remaining water is dripping off evaporator
5. Drain delay (Hot gas only): where the drain valve is opened to drain the liquid refrigerant
6. Fan delay: where the fans are restarted when the remaining water on the evaporator has turned into ice
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