Danfoss AK-PC 781A, User Manual, Page: 33 / 138

AK-PC 781A Capacity controller RS8HE202 © Danfoss 2017-07 33
A bit more about the functions
Compressor
Regulation of up to 10 compressors. And up to 3 unloaders each
compressor.
Compressor No. 1 or 2 can be speed-regulated.
The following can be used as control sensor:
1) P0 - Suction pressure
2) S4 - Cold brine temperature
3) Pctrl - Condensing pressure in the low pressure circuit controls
the high-pressure circuit for cascade control.
(P0 is also used for 2 and 3, but for low-pressure safety.)
Condenser
Regulation of up to 8 condenser steps.
Fans can be speed-regulated. Either all on one signal or only the
first fan of several. EC motor can be used.
Relay outputs and solid state outputs may be used, as desired.
The following can be used as control sensor:
1) Pc - Condensing pressure
2) S7 - Warm brine temperature (Pc is used here for high-pressure
safety.)
3) Sgc -Temperature at the gas cooler outlet.
Connection between high-pressure and low-pressure circuits
(MT and LT circuits)
Capacity control of the high-pressure circuit can be adjusted by
the condensing pressure in the low-pressure circuit.
The controller can give off a signal from a relay output so that the
low-pressure circuit can only start when the high-pressure circuit
is on.
The controller can receive a signal from the low-pressure circuit
that there is a need for refrigeration.
Coordination is also required for parallel compression.
Speed regulation of condenser fans
The function requires an analog output module.
A relay output may be used for start/stop of the speed regulation.
The fans may also be cut in and out by relay outputs.
Trouble-shooting function FDD on condenser x
Condenser pressure reference
Floating condensing pressure reference
x
Setting of references for heat recovery functions x
Safety functions
Min. suction pressure
x
Max. suction pressure x
Max. condensing pressure x
Max. discharge gas temperature x
Min. / Max. superheat x
Safety monitoring of compressors x
Common high pressure monitoring of compressors x
Safety monitoring of condenser fans x
General alarm functions with time delay 10
Miscellaneous
Extra sensors
7
Inject On function x
Option for connection of separate display 4 + 1
Separate thermostat functions 5
Separate pressostat functions 5
Separate voltage measurements 5
PI regulation 3
Max. input and output 120
Pulse wide modulating unloading
When using a compressor with PWM-unloading, the unloading should
be connected to one of the four solid state outputs in the controller.
Heat recovery
There are adjustment options for hot water and heat containers
for heating.
The controller manages, in order of priority: 1 -tap water 2-heating
3-gas cooler, which removes the remaining excess heat.
Safety circuit
If signals are to be received from one or more parts of a safety
circuit, each signal must be connected to an ON/OFF input.
Day/night signal for raising the suction pressure
The clock function can be used, but an external ON/OFF signal
may be used instead.
If the “P0 optimization” function is used, no signal will be given
concerning the raising of the suction pressure. The P0 optimiza-
tion will see to this.
“Inject ON” override function
The function closes expansion valves on evaporator controls when
all compressors are prevented from starting.
The function can take place via the data communication, or it may
be wired via a relay output.
Separate thermostat and pressure control functions
A number of thermostats can be used according to your wishes.
The function requires a sensor signal and a relay output. In the
controller there are settings for cutin and cutout values. An associ-
ated alarm function may also be used.
Separate voltage measurements
A number of voltage measurements can be used according to
your wishes. The signal can for example be 0-10 V. The function
requires a voltage signal and a relay output. In the controller there
are settings for cutin and cutout values. An associated alarm func-
tion may also be used.
If you want to know more about the functions, go to
chapter 5.
Connections
Here is a survey of the possible connections. The texts can be read in
context with the table on the following page.
Analog inputs
Temperature sensors
• S4 (Cold brine temperature)
Must be used when the control sensor for compressor control has been
selected as S4.
• Ss (suction gas temperature)
Must always be used in connection with compressor regulation.
• Sd (discharge gas temperature)
Must always be used in connection with compressor regulation.
3 • Sc3 (outdoor temperature)
To be used when monitoring function FDD is used.
To be used when regulation is performed with floating condenser refer-
ence.
• S7 (warm brine return temperature)
Must be used when the control sensor for condenser has been selected
as S7.
• Saux (1-4), any extra temperature sensors
Up to four additional sensors for monitoring and data collection may be
connected. These sensors can be used for general thermostat functions.
• Stw2, 3, 4 and 8 (temperature sensors for heat recovery)
Must be used when adjusting hot tap water.
Shr2, 3, 4 and 8 (temperature sensors for heat recovery)
Must be used when adjusting the heat receiver for heating.