22 Technical brochure RC8CF102 © Danfoss 08-2014 AK-PC 551
Frequently asked questions (FAQ)
Question Solution
How to connect
variable speed drive
(VSD)?
The analogue outputs AO3 and AO4 of the AK-PC 551 pack
controller is galvanic separated from the other inputs and outputs
of the controller� So if the AK-PC 551 controller is ordered for 24Vac
supply voltage, you can use the same 24Vac transformer for power
supply of the controller and for supply of the analogue outputs�
It is recommended to use a double isolated transformer (Class II) as
this type does not need to be connected to protective earth on the
secondary side� This will prevent any ground loops between the
AK-PC 551 pack controller and the variable speed drive connected
to AO3 or AO4�
Example: Variable speed drive connected
to AO3
How to connect the
PWM valve of a digital
scroll compressor?
The Pulse Width Modulated valve (PWM) of a digital scroll
compressor must be connected to one of the solid state relays
(SSR) of AK-PC 551 - which are the outputs DO5 or DO6� The PWM
valve function cannot be selected for any of the other digital
outputs�
The PWM valve of the digital scroll compressor works in such a
way that when voltage is supplied to the valve, the digital scroll
compressor is unloaded and when no voltage is supplied to the
valve, the digital scroll compressor is loaded�
When the PWM valve signal is selected for DO5 or DO6, the
polarity of the output signal is by default inverted and thereby
the PWM valve of the digital scroll compressor can be connected
directly to the AK-PC 551 without any intermediate relays�
Example: Wiring of PWM valve of digital
scroll compressor to DO5/DO6 of AK-PC
551
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