Mitsubishi Electric City Multi PQHY-P72 Service Handbook page 275

[ IX Troubleshooting ]
(3) Check method and remedy
1) Measures against noise
Check the followings when noise exists on the wave or the errors described in (1) occur.
Check 1. The transmission line and the power
that the 208 / 230 V line are not wired too
wiring closely.
work is
2. The transmission line is not bundled
per-
with that for another systems.
formed
accord-
ing to wir-
3. The specified wire is used for the
ing
transmission line.
specifica-
tions.
4. When the transmission line is daisy-
chained on the indoor unit terminals,
are the shields daisy-chained on the
terminals, too?
Check 5. Is the grounding of the shield of the
that the transmission line (for indoor unit con-
ground- trol) provided on the indoor unit?
ing work
is per-
6. Check the treatment method of the
formed
shield of the transmission line (for cen-
accord-
tralized control).
ing to
ground-
ing speci-
fications.
Error code definition
- 266 -
Remedy
Isolate the transmission line from the power line (5cm [1-31/
32"] or more). Do not insert them in the same Do not insert
them in the same conduit.
The transmission line must be isolated from another transmis-
sion line.
When they are bundled, erroneous operation may be caused.
Use the specified transmission line.
Type: Shielded wire CVVS/CPEVS/MVVS (For M-NET re-
mote controller)
2
Diameter: 1.25mm [AGW16] or more
(Remote controller wire: 0.3 - 1.25mm
The transmission is two-wire daisy-chained. The shielded
wire must be also daisy-chained.
When the shielded cable is not daisy-chained, the noise can-
not be reduced enough.
One point grounding must be provided on the heat source
unit. If no grounding is provided, the noise on the transmission
line cannot escape leading to change of the transmission sig-
nal.
When group operation of indoor units connected to different
heat source units is performed, provide grounding of the
shield of the transmission line for centralized control at the
point of heat source unit, and when the system controller is
used, provide grounding at the point of the system controller,
so that the effect of noise can be minimized.
The environment against noise varies depending on the dis-
tance of the transmission lines, the number of the connected
units, the type of the controllers to be connected, or the envi-
ronment of the installation site. Therefore, the transmission
line work for centralized control must be performed as follows.
(1) When no grounding is provided
Group operation of indoor units connected to different
heat source units: One point grounding on one heat
source unit (power supply unit)
Use of MELANS: Grounding on the main controller
(power supply device)
(2) When an error occurs even though one point grounding
is provided: Ground the shield on all heat source units.
2
[AGW22-16])