AK-PC 772A
Capacity
controller RS8HF102 © Danfoss 2017-07
111
Supply voltage
If the power supply to AK-PC 772A or the high pressure valve Vhp
fails, the system cannot be controlled. We recommend installing
an emergency supply (UPS) for both the controller and the valve
to avoid faults. A relay in the UPS should be incorporated into the
controllers safety circuit so that it can restart safely.
Main switch
The main switch is used to stop and start the controlling function.
The switch-over has 2 positions:
- Normal controlling state (Setting = ON)
- Control stopped. (Setting = OFF)
In addition, one can also choose to use a digital input as an
external main switch.
If the switch-over or the external main switch is set at OFF, all the
control’s functions are inactive and an alarm is generated to draw
attention to this – all other alarms cease.
External switch for stopping compressors
The switch will stop the compressors, but all other functions will
continue to be regulated.
Refrigerant
For CO2 only
Sensor failure
If lack of signal from one of the connected temperature sensors or
pressure transmitters is registered an alarm will be given.
• When there is a P0 error regulation will continue with 50% cut-in
capacity during day operation and 25% cut-in capacity during
night operation – but minimum one step.
• When there is a Pc error 100% condenser capacity will be cut in,
but the compressor regulation will remain normal.
• When there is an error on the Sd sensor the safety monitoring of
the discharge gas temperature will be discontinued.
• When there is an error on the Ss sensor the monitoring of the
superheat on the suction line will be discontinued.
• When there is an error on the outdoor temperature sensor Sc3
the Pc value is used as reference.
Note: An incorrect sensor must be in order for 10 minutes before
the sensor alarm deactivates.
Safety disconnection signal
Unexpected disconnection of the compressor, condensation fan
or frequency convertor can result in unexpected temperature
increases in the system. If necessary, use the necessary safety
signals to ensure that the controller receives signals about discon-
nections.
Sensor calibration:
The input signal from all connected sensors can be corrected. A
correction will only be necessary if the sensor cable is long and
has a small cross-sectional area. All displays and functions will
reflect the corrected value.
Clock function
The controller contains a clock function.
The clock function is used only to change between day/night.
The year, month, date, hour and minutes must be set.
In the event of a power failure, the time setting will be remembe-
red for at least 12 hours.
If the controller is connected to an installation with an AKA-
gateway or an AK system manager, this will automatically reset
the clock function.
Alarms and messages
In connection with the controller’s functions, there are a number
of alarms and messages that become visible in cases of fault or
erroneous operation.
Alarm history:
The controller contains an alarm history (log) that contains all
active alarms as well as the last 40 historical alarms. In the alarm
history you can see when the alarm began and when it stopped.
In addition, one can see the priority of each alarm as well as when
the alarm has been acknowledged and by which user.
Alarm priority:
Differentiation is made between important and not-so-important
information. The importance – or priority – is set for some alarms
whilst others can be changed voluntarily (this change can only
be done with attachment of AK-ST service tool software to the
system and settings must be made in each individual controller).
The setting decides which sorting / action must be carried out
when an alarm is sounded.
• “High” is the most important
• “Log only” is the lowest
• “Interrupted” results in no action
Alarm relay
One can also choose whether one requires an alarm output on
the controller as a local alarm indication. For this alarm relay it is
possible to define on which alarm priority it must react to – one
can choose between the following:
• “Non” – no alarm relay is used
• “High’ – Alarm relay is activated only with alarms with high
priority
• “Low - High’ – Alarm relay is activated only with alarms with “low”
priority, “medium” or “high” priority.
Miscellaneous
