Carrier 42QFD048D8S Service Manual page 89

TS02-L-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:
S Communication:
Power off, then restart the unit after 2
Check the wiring connection
between indoor and outdoor
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
output to IPM board, is it same
components connected to main
PCB such as 4 way valve, heater,
AC fan one by one to check their
resistance. Is there any component
Unplug electronic expansion valve.
Check if the DC 5V, 12V to main
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.
minutes.
Does the error code
No
disappear?
Yes
No
unit, are they good?
Yes
The value is fixed and close
The value is always positive
For units without W
wire
Check the wiring connection
both
Check the AC voltage of L, N
No
as power input?
Yes
Unplug all the high voltage
Yes
short circuit?
No
Check the DC 5V, 12V
from IPM board to main
PCB, are they normal?
No
Yes
PCB are OK
No
Replace IPM board

Solved
Correct the connection or
change wires
The value is alternative
from negative to positive
to 0
For units
with W wire
from outdoor terminal to
outdoor PCB and wiring
For units with only one
between PCBs if there is
PCB
more than 1 PCB
Replace main PCB Replace outdoor PCB
Replace short-circuited
component and main
PCB
Yes
Replace short-circuited
component and outdoor
PCB
Replace coil of electronic
expansion valve
Troubleshooting
Check the wiring connection
from indoor terminal to indoor Repalce indoor PCB
PCB, are they good?
Turn on the unit, check if W
and 1(L) is connected?
Yes
Check if the power LED is
Yes
on?
No
Unplug all the high voltage
components connected to main
PCB such as 4 way valve, heater,
Yes
AC fan one by one to check their
resistance. Is there any component
No
short circuit?
No
Unplug electronic expansion valve.
Yes
Check if power LED is on?

No