40MBAB: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
18
DIAGNOSIS AND SOLUTION (CONT.)
(S) Current Loop Communication:
Note: For certain models, outdoor PCB could not be removed separately. In this case, the outdoor electric control box should be
replaced as a whole.
Does the error code
disappear?
Power off, then restart the unit af ter 2
minutes.
Measure the DC voltage between N/L2
and S (Black pin to S , Red pin to N/L2).
The value is fixed and close
to 0
The value is alt ernative
from negat ive to posit ive
The value is alw ays posit ive
Check t he w iring connection
bet ween indoor and out door
unit, are t hey good?
Check t he w iring connection
from outdoor terminal t o
outdoor PCB and wiring
bet ween PCBs if t here is
more t han 1 PCB
Check t he w iring connection
from indoor terminal t o indoor
PCB, are t hey good?
Check if t he pow er LED is
on?
Yes
Yes
Unplug all the high voltage
components connected t o main
PCB such as 4 way valve, heater,
AC f an one by one t o check their
resist ance. Is there any component
short circuit?
Unplug elect ronic expansion valve.
Check if pow er LED is on?
No
No
Check t he AC volt age of L, N
output t o IPM board, is it same
as pow er input?
Check t he DC 5V, 12V
from IPM board t o main
PCB, are t hey normal?
Unplug all the high voltage
components connected t o main
PCB such as 4 way valve, heater,
AC f an one by one t o check their
resist ance. Is there any component
short circuit?
Yes
No
Unplug elect ronic expansion valve.
Check if t he DC 5V, 12V to main
PCB are OK
Replace short-circuited
component and main
PCB
Replace coil of elect ronic
expansion valve
Replace out door PCB
Replace short-circuited
component and outdoor
PCB
Yes
Yes
Yes
Yes
Replace main PCB
No
Yes
No
Replace IPM board
No
Repalce indoor PCB
Solved
Correct the connection or
change w ires
No
No
Yes
For unit s with main PCB and IPM board
both
For unit s with only one
PCB
No