5. Connecting the indoor unit
During the first 30 seconds after mains power to the outdoor unit is switched on the UC8 controller
searches for a connection to an indoor unit. The indoor unit must send a reply to the outdoor unit
withing that first half minute. The outdoor unit will not continue attempting to contact the indoor unit
if no reply is received from the indoor unit within those first 30 seconds.
To ensure the indoor unit is ready to reply to the outdoor unit it is important that power to the indoor
unit must be applied either at the same time, or before, the outdoor unit.
5.1. Making a reliable connection between the outdoor- and indoor- unit
In most split air-conditioning installations the UC8 controller in the outdoor unit communicates with
an IUC (indoor unit controller) in the indoor unit. For reliable operation the connection should be
made using a shielded twisted pair cable. The twisted pair wires must be used for signals A and B. The
cable shield can be connected to the 0V terminal at the UC8 only.
Using a shielded twisted pair cable helps to reduce electrical interference from other nearby cabling:
• the cable shield reduces interference from electric fields generated by mains voltages
• using a twisted pair of wires reduces interference from magnetic fields that surround any
cables that carry electrical currents
IMPORTANT: The communications ports on the UC8 and on the IUC use the unit earth as reference;
the ports are not electrically isolated. For that reason it is important that there is a direct and solid
earth connection between the outdoor- and the indoor- units.
5.2. Connecting 1 outdoor unit to 1 indoor unit
The diagram below shows standard connections between outdoor- and indoor- units.
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