Danfoss AK-CC 421 User guide
User Guide
Controller for Condensing unit
AK-CC 421
Introduction
Application
Condensing unit control
Advantages
• Condensing pressure control in relation to outside temperature
• Fan variable speed regulation
• On/off or variable speed regulation of the compressor
• Heating element control in crankcase
• Day/night controller operation
• Built-in clock function with power reserve
• Built-in Modbus data communication
• Monitoring discharge temperature td
• Oil return management control at variable speed control
Principle
The controller receives a signal for demanded cooling, and it then
starts the compressor.
If the compressor is controlled by variable speed, the suction pressure (converted to temperature) will be controlled according to a
set temperature value.
Condenser pressure regulation is performed again following a
signal from the ambient temperature sensor and the set reference.
The controller will then control the fan, which allows the condensing temperature to be maintained at the desired value.
The controller can also control the heating element in the crankcase so that oil is kept separate from the refrigerant.
For excess discharge temperature, the liquid injection will be activated in the suction line.
Functions
• Control of condensing temperature
• Control of fan speed
• On/off control or speed regulation of the compressor
• Control of heating element in crankcase
• Liquid injection into economizer port
• Raising the condenser pressure regulation reference during night
operation
• Safety cut-out activated via signal from automatic safety control
Regulation reference for condensing temperature
The controller controls the condensing temperature in relation
to the ambient temperature. A set point is entered for how much
higher the reference must be. The reference can be raised at night.
Day/Night
The controller has an internal clock function which changes
between daytime and night operation.
During night operation, the reference is raised by the 'Night offset'
value.
This day/night signal can also be activated in two other ways:
• Via an on/off input signal - DI2
• Via data communication.
Set Point
Reference
Tamb
Day
Night offset
Night
Day
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Fan operation
The controller will control the fan so that the condensing
temperature is maintained at the desired value above the outdoor
temperature.
The user may select from different ways to control the fan:
• Internal speed regulation
Here the fan is speed-controlled via terminal 5-6.
At a need of 95% and above, the relay on terminal 15-16 are
activated, while 5-6 are deactivated.
• External speed regulation
For larger fan motors with insufficient internal outlet, an external
speed regulation can be connected to terminal 54-55. A 0-10 V
signal indicating the desired speed is then sent from this point.
The relay on terminal 15-16 will be active when the fan is in
operation.
In menu 'F17' the user can define which of the two controls to use.
Fan speed at start
When the fan is re-started after an idle period, it will be started
at a speed that is set in the 'Jog Speed' function. This speed is
maintained for 10 seconds, after which the speed changes to the
regulation need.
Fan speed at low loads
At low loads between 10 and 30%, the speed will remain at that
which is set in the 'FanMinSpeed' function.
Fan speed at low ambient temperatures
To avoid frequent start/stops in low ambient temperatures in
which the fan's capacity is high, the internal amplification factor is
lowered. This provides a smoother regulation.
The 'Jog speed' is also lowered in the area from 10°C and down to
-20°C.
At temperatures below -20°C the 'Jog Low' value can be used.
Speed
Jog
Min.
Speed
Jog low
Jog
Required
capacity
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Compressor control
The compressor is controlled by a signal at the DI1 input.
The compressor will start once the input is connected.
Three restrictions have been implemented to avoid frequent start/
stops:
- One for minimum ON time
- One for minimum OFF time
- One for how much time must elapse between two starts.
These three restrictions have the highest priority during
regulation, and the other functions will wait until they are
complete before regulation can continue. When the compressor is
'locked' by a restriction, this can be seen in a status notification.
If the DI3 input is used as a safety stop for the compressor, an
insufficient input signal will immediately stop the compressor.
The compressor can be speed-controlled with a voltage signal at
the AO2 output.
If the compressor has been running for a long period at low speed,
the speed is increased for a short moment for the purpose of oilreturn.
Maximum discharge gas temperature
The temperature is recorded by sensor Td.
If variable speed control is chosen for the compressor, this control
will initially reduce the compressor capacity if the Td temperature
approaches the set maximum value.
If a higher temperature is detected than the set max. temperature,
the fan's speed will be set to 100%. If this does not cause the
temperature to drop, and if the temperature remains high
after the set delay time, the compressor will be stopped. The
compressor will only be re-started once the temperature is
10 K lower than the set value. The above mentioned re-start
restrictions must also be complete before the compressor can
start once again.
If the delay time is set to '0', the function will not stop the
compressor. The Td sensor can be deactivated (o63).
Liquid injection into economizer port
The controller can activate the liquid injection into economizer
port if the discharge temperature is approaching the maximum
allowable temperature.
Note: Liquid injection function use the Aux Relay.
High pressure monitoring
During regulation, the internal high pressure monitoring function
is able to detect an over the limit condensing pressure so that the
regulation can continue.
However, if the C73 setting is exceeded, the compressor will be
stopped.
If, on the other hand, the signal comes from the interrupted safety
circuit connected to DI3, the compressor will immediately be
stopped and the fan will be set to 100%.
When the signal is once again 'OK' at the DI3 input, the regulation
will resume.
Low pressure monitoring
During regulation, the internal low pressure monitoring function
will cut out the compressor upon detecting a suction pressure that
falls below the lower limit, but only once the minimum ON time
is exceeded. An alarm will be issued. This function will be time
delayed, if the compressor starts at low ambient temperature.
Pump down limit
The compressor will be stopped if a suction pressure that falls
below the set value is registered, but only once the minimum ON
time is exceeded.
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Heating element in the crankcase
The controller has a thermostat function which can control the
heating element for the crankcase. Oil can thus be kept separate
from the refrigerant. The function is active when the compressor
has stopped.
The function is based on the ambient temperature and suction
gas temperature. When the two temperatures are equal ± a
temperature difference, power will be supplied to the heating
element.
The 'CCH off diff' setting indicates when power will no longer be
supplied to the heating element.
The 'CCH on diff' indicates when 100% power will be sent to the
heating element.
Between the two settings the controller calculates the wattage
and connects to the heating element in a pulse/pause cycle which
corresponds to the desired wattage.
The Taux sensor can be used to record the temperature in the
crankcase if desired.
When the Taux sensor records a temperature lower than Ts+10 K,
the heating element will be set to 100%, but only if the ambient
temperature is below 0°C.
Digital inputs
There are two digital inputs DI1 and DI2 with contact function and
one digital input DI3 with high voltage signal.
They can be used for the following functions:
DI1: Starts and stops compressor
DI2: Here the user can select from various functions
Status notification from an external safety function
External main switch
Night setback signal
Separate alarm function
Monitoring of input signal
DI3: Safety signal from low/high-pressure switch
Data communication
The controller is delivered with built-in MODBUS data
communication.
If a different form of data communication is requested, a LON RS485 module can be inserted in the controller.
The connection will then be made on terminal RS 485.
Important
All connections to the data communication must comply with the
requirements for data communication cables.
See literature: RC8AC.
Display
The controller has one plug for a display. Here display type EKA
163B or EKA 164B (max. length 15m) can be connected.
EKA 163B is a display for readings.
EKA 164B is both for readings and operation.
The connection between display and controller must be with a
cable which has a plug at both ends.
A setting can be made to determine whether the Tc or Ts is to be
read out. When the value is read out, the second read-out can be
displayed by briefly pressing the lower button.
When a display is to be connected to the built-in MODBUS, the
display can advantageously be changed to one of the same type,
but with Index A (version with screw terminals).
The controllers address must be set higher than 0 in order for the
display to be able to communicate with the controller.
If connection of two displays is required, one must be connected
to the plug (max. 15 m) and the other must then be connected to
the fixed data communication.
Address o03 > 0
Override
The controller contains a functions which can be used together
with the override function in the master gateway/system manager.
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Function via data communication Day/Night schedule
Function in gateway/system manager Day/Night control / Time
schedule
Used parameters in AK-CC 421 --- Night setback
Survey of functions
Function Para-
meter
Normal display
The display shows the temperature value for the suction pressure Ts or from the condensing pressure Tc. Enter which of the two are to be displayed in o17.
During operation, when one of the two is shown in the display, the other value can be
seen by pressing and holding in the lower button.
Thermostat Thermostat control
Set point
The controller's reference Tc is the outside temperature + set point + any applicable
offset.
Enter the set point by pressing the middle button. A offset can be entered in r13.
Unit
Set here if the display is to show SI-units or US-units
0: SI (°C and bar)
1: US (°F and Psig).
Start / stop of refrigeration
With this setting refrigeration can be started, stopped or a manual override of the
outputs can be allowed. (For manual control the value is set at -1. Then the relay outlets can be force-controlled by the respective reading parameters (u58, u59 etc.). Here
the read value can be overwritten.)
Start / stop of refrigeration can also be accomplished with the external switch function connected to a DI input.
If the external switch function is deselected, the input must be shorted.
Stopped refrigeration will give a ”Standby alarm”.
Night setback value
The controller reference is raised by this value when the controller switches to night
operation.
Reference Ts
Here the reference is entered for the suction pressure Ts in degrees.
Reference Tc
Here the current controller reference for condensing pressure Tc can be read out in
degrees.
Minimum condensing temperature (lowest permitted regulation reference)
Here the lowest permitted reference is entered for the condensing temperature Tc.
Maximum condensing temperature (highest permitted regulation reference)
Here the highest permitted reference is entered for the condensing temperature Tc.
Maximum discharge gas temperature
Here the highest permitted discharge gas temperature is entered. The temperature
is measured by sensor Td. If the temperature is exceeded, the fan will be started at
100%. A timer is also started which can be set in c72. If the timer setting runs out,
the compressor will be stopped and an alarm will be issued. The compressor will be
reconnected 10 K below the cut-out limit, but only after the compressor's off timer
has expired.
Alarm Alarm settings
The controller can give alarm in different situations. When there is an alarm all the
light-emitting diodes (LED) will flash on the controller front panel, and the alarm relay
will cut in.
Delay of a DI2 alarm
A cut-out/cut-in input will result in alarm when the time delay has been passed. The
function is defined in o37
High condensing temperature
The limit value (difference over normal reference) to which the condensing temperature has increased, and at which an alarm must be issued. Can be set in K.
Delay time for alarm A70. Set in minutes. A71 Air flow del
Parameter by operation via data
communication
Ts / Tc
Reference
r05 Unit
°C=0. / °F=1
(Only °C on AKM, whatever the setting)
r12 Main Switch
1: Start
0: Stop
-1: Manual control of outputs allowed
r13 Night offset
r23 Ts Ref
r29 Tc Ref
r82 MinCondTemp
r83 MaxCondTemp
r84 MaxDischTemp
Night setbck
(start of night signal. 0=Day, 1=Night)
With data communication the importance of the individual alarms can be
defined. Setting is carried out in the
“Alarm destinations” menu via AKM.
A28 AI.Delay DI2
A70 Air flowDiff
Reset alarm
Ctrl. Error
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