AK-CC 750 - 080Z0130 & 080Z0139
RS8GM222 © Danfoss 10-2014
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first section of a controller has finished defrost, the controller starts
the “Max. hold time” function and when all sections have finished
defrost, this is recorded by the system unit. The controller will
then move into waiting position until it receives a signal to restart
refrigeration. This happens when all controllers in the group have
concluded their defrosts. If this message has not been received
within the “Max. holding time” time, the controller will resume
refrigeration under all circumstances.
Drip-off delay (state 5)
A time delay can be put in so that any drops of water may drip
off the evaporator before refrigeration is resumed. In this way it is
ensured that the evaporator as far as possible is free from water
when refrigeration is restarted.
Drain delay / pressure equalisation during hot gas defrost
(state 6)
When the drip delay is completed, it is possible to add a drain
delay in which the smaller drain valve opens up to the suction line
so that pressure equalisation takes place. Once the drain delay has
expired, the main valve in the suction line opens and cooling is
resumed.
Delayed fan start (state 7)
Regardless of whether the fans are running or have stopped
during the defrost sequence, the fans can be stopped during this
delay.
Drops of water left on an evaporator after defrost should be bound
to the evaporator (primarily used in freezing rooms).
After defrost, the liquid injection is started, the evaporator is
cooled down, but the fans will be started a little later. During this
period the controllers operate the expansion valve by force, but
they constantly monitor the superheat.
The temperature at which the fans are to be started is set (meas-
ured always with the S5 sensors). The max. permissible time delay
in minutes is set.
The time delay for fan start will not commence until the time delay
for liquid injection, if applicable, has run out.
Only when all the S5 sensors register a lower temperature than the
set will the fans be started. If all S5 sensors do not register a lower
temperature than the set by the delay time has elapsed, the fans
will start. At the same time alarm is given that Maximum delay
time for fan is exceeded for the section in question. If the alarm
is not acknowledged within five minutes, it will automatically be
cancelled.
If some of the S5 sensors are defective, the signal from sensors that
remain intact will be used.
Example
Below is an example of a defrost sequence using hot gas defrost.
The following are used in the example:
- Hot gas defrost with common hot gas valves
- Defrost using the evaporators is stopped individually using the
S5 temperature
- The fans are stopped during defrost
The defrost sequence will be as follows:
• Pump down (state 1)
The AKV valve closes, the heating element in the drip tray is
activated and the fans run.
• Defrost (state 3)
The fans stop, the main valve and the drain valve in the suction
line are closed and the hot gas valve opens.
Defrost is terminated when the S5 sensor has reached its stop
temperature.
• Hold (state 4)
If coordinated defrost is being used, the controller will wait for
a release signal from the network's system unit before continu-
ing with the sequence. Alternatively, the hold stops once the
maximum hold time has expired.
• Drip delay (state 5)
Cooling is delayed so that any drops of water can run off the
evaporator.
• Drain delay / pressure equalisation (state 6)
The drain valve opens so that pressure equalisation takes place
in the evaporator.
• Fan delay (state 7)
The main valve in the suction line opens and liquid injection is
resumed. The fans are delayed so that the remaining drops of
water are bound to the evaporator. The fans start when the re-
quired fan start temperature has been reached on the S5 sensor,
or when the set delay time has expired.
