AK-PC
551
User
Guide RS8GY302 © Danfoss 2015-06
5
Safety functions
Min./max. suction pressure Po
The suction pressure is recorded continuously.
If the measured value falls below the set minimum limit,
the compressors will immediately cut out.
If it exceeds the max. value, an alarm will be generated once
the time delay has elapsed.
Max. condensing pressure Pc
If the condensing pressure reaches the upper permissible value,
the controller will connect all condenser fans to keep the pressure
down. At the same time, a portion of the compressor capacity will
be disconnected. If the pressure remains near the threshold value,
even more compressors will be disconnected.
All compressors will be disconnected immediately if the threshold
value is exceeded.
LP switch
On/off signal on a DI input
If a signal is received, all compressors will immediately be stopped.
HP switch
On/off signal on a DI input
If a signal is received, all compressors will immediately be stopped.
Fan capacity will increase depending on how much the
Pc measurement exceeds the reference.
Min./max superheating via Ss measurement
Temperature sensor on an AI input.
If superheating is higher or lower than the set limits, an alarm
will be generated once the time delay has elapsed.
Max. discharge gas temperature Sd
Temperature sensor on an AI input.
A signal can be received from a Pt 1000 Ohm sensor on
the pressure pipe.
• Common Sd for the whole compressor group
If the temperature nears the set max. temperature, the capacity
of the compressor will be reduced
• Compressor Sd
if it is an Sd from a Copeland digital scroll, a Copeland stream or
Bitzer CRII the capacity will be increased so that the compressor
can cool down itself).
The compressors will be stopped if the temperature nears
the set max. temperature value.
Sensor failure
If lack of signal from one of the connected temperature sensors or
pressure transmitters is registered an alarm will be given.
• In the event of a Po error, regulation will continue with a set
capacity in daytime operation (e.g. 50%), and a set capacity in
night operation (e.g. 25%), but with a minimum of one step.
• In the event of a Pc error, the condenser capacity that
corresponds to how much compressor capacity is connected
will cut in. 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.
• In the event of an error on the outdoor temperature sensor,
Sc3, the permanent setting value will be used as a reference.
• In the event of an error on the S4 sensor, regulation will continue
with the Po signal, but the reference will be lowered by 5 K.
• In the event of an error on the Saux sensor, the thermostat
output will go to the rest position.
NB: A faulty sensor must be OK within 10 minutes before a sensor
alarm is cancelled.
A sensor alarm can be reset manually by pushing the "X-
button" for 2 seconds when the alarm is shown in the display
"Active alarms".
General DI alarms
On/off signal on a DI input
The regulator contains three general alarm inputs, to which alarm
text and delay times can be connected.
Alarm and text will appear when the delay time has elapsed.
General thermostat
It is possible to install one general thermostat if there is a relay
output and an analogue input available.
