COMFORT-AIRE Century VMH-SV Series Service Manual page 122

TS02-S-INV: Indoor and outdoor unit communication error diagnosis and solution
Description: Indoor unit can not communicate with outdoor unit
Recommended parts to prepare:
• Indoor PCB
• Outdoor PCB
• Short-circuited component
Troubleshooting and repair:
Power off, then restart the unit after 2
minutes.
Does the error code
disappear?
Check the wiring connection
between indoor and outdoor
unit, are they good?
Measure the DC voltage between N/L2
and S (Black pin to N/L2, Red pin to S).
For units with main PCB and IPM board
Check the AC voltage of L, N
output to IPM board, is it same
as power input?
Unplug all the high voltage
components connected to main
PCB such as 4 way valve, heater,
AC fan one by one to check their
resistance. Is there any component
Check the DC 5V, 12V
from IPM board to main
PCB, are they normal?
Unplug electronic expansion valve.
Check if the DC 5V, 12V to main
Replace IPM board
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.
Solved
Yes
No
Correct the connection or
No
change wires
The value is alternative
from negative to positive
Yes
The value is fixed and close
to 0
The value is always positive
For units without W
wire
Check the wiring connection
from outdoor terminal to
both
outdoor PCB and wiring
between PCBs if there is
more than 1 PCB
No Replace main PCB
Yes
Yes
short circuit?
Yes
No
No
Yes
PCB are OK
No
Troubleshooting

Troubleshooting
Check the wiring connection
from indoor terminal to indoor
PCB, are they good?
For units
with W wire
Turn on the unit, check if W
and 1(L) is connected?
Yes
For units with only one
PCB
Replace outdoor PCB Yes
Replace short-circuited
component and main
PCB
Replace short-circuited
component and outdoor Yes
PCB
No
Replace coil of electronic
Yes
expansion valve

Repalce indoor PCB
No
Check if the power LED is
on?
No
Unplug all the high voltage
components connected to main
PCB such as 4 way valve, heater,
AC fan one by one to check their
resistance. Is there any component
short circuit?
No
Unplug electronic expansion valve.
Check if power LED is on?