Midea MVC-670WV2GN1 - Page 183

VC Pro VRF 50/60Hz
183
Part 3 - System Design and Installation
9.3 Communication Wiring
Communication wiring design and installation should adhere to the following requirements:
 0.75mm
2
three-core shielded cable should be used for communication wiring. Using other types of cable can lead to
interference and malfunction.
 Indoor communication wiring:
 The P Q E communication wires should be connected one unit after another in a daisy chain from the outdoor unit
to the final indoor unit as shown in Figure 3-9.4. At the final indoor unit, a 120Ω resistor should be connected
between the P and Q terminals. After the final indoor unit, the communication wiring should NOT be continued
back to the outdoor unit – that is, do not attempt to form a closed loop.
 The P and Q communication wires should NOT be grounded.
 The shielding nets of the communication wires should be connected together and grounded. Grounding can be
achieved by connecting to the metal casing adjacent to the P Q E terminals of the outdoor unit electrical control
box.
 Outdoor communication wiring:
 The H1 H2 E communication wires should be connected one unit after another in a daisy chain from the master
outdoor unit to the final slave outdoor unit as shown in Figure 3-9.4.
Figure 3-9.4: Communication wiring configurations – correct and incorrect examples
√
Master
unit
Slave
unit
Slave
unit
H1 H2 E H1 H2 E
P Q E
P Q E
P Q E P Q E P Q E
P
Q
120Ω resistor
between PQ
×
Master
unit
Slave
unit
Slave
unit
P Q E
P Q E
H1 H2 E
H1 H2 E
P Q E P Q E P Q E P Q E