Mds System Wiring; Wiring Connection Between Mds Outdoor To Indoor Units - McQuay MDS Series Service Manual

3.3 MDS System Wiring

The wiring for MDS is very critical as MDS is a system by itself. Generally, the wiring connection can be divided
into wiring connection between MDS outdoor to indoor units, wiring connection between MDS outdoor units and
wiring connection between MDS master and slave unit. The wire used for all will be the same.
3
A screen cable is recommended because the screen cable will help to filter the electrical noise along the
communication wiring and thus help to maintain stability on the communication. For the MDS system, the
communication protocol is using RS485. The wire length between first outdoor to last outdoor must not exceed
1000m, and the wire length between outdoor to last indoor also must not exceed 1000m.

3.3.1 Wiring Connection Between MDS Outdoor to Indoor Units

As the MDS system is a single outdoor multiple indoors system, it is required to have communication wiring
between the outdoor and all indoors. The wiring is required to be connected serially (Daisy chain) inside a
conduit. Please take note that the communication wiring cannot mix inside a same conduit with power supply.
For outdoor model, there are two type of outdoor board (MDOM PCB and MDS-M PCB). However, the wiring
connection for both PCB is basically the same. There are two wiring connectors located on the PCB, one of it is
green color and the other is orange color. For outdoor to indoor communication, the communication wires need
to be connected to the green terminal. The labels of the terminals are A
18
Outdoor Outdoor
A A B B
Last Indoor Unit,
Jumper JP1 need
to be shorted
A A
Indoor 1 Indoor 1
B B
A A
Indoor 2 Indoor 2
B B
A A
Indoor N Indoor 3
B B
and B .
in in
Service Manual SM-MDS_(ii)