Carrier 619FB Service Manual page 42

9. Communication malfunction (AP1 below is control board of the outdoor unit).
Main detection points:
S Check if the connection wire and the built- -in wiring of the indoor and the outdoor unit is connected well and not damaged.
S Is the communication circuit of the indoor mainboard damaged? Is the communication circuit of the outdoor mainboard (AP1)
damaged?
Malfunction diagnosis process:
Malfunction of
circuit is
detected with
control board
AP1 voltage
Does
the unit operate
normally?
Y
Yes
Check built-
in wiring of
indoor and
outdoor unit
Is the wiring
Yes
damaged?
No
Check communication
No
circuit of outdoor unit
Problem with
communication
circuit
No
Replace indoor
board
Fig. 45 – Troubleshooting
Start
If the unit is operation
normal before malfunction
Y
Yes
Replace outdoor
Yes
Y
mainboard AP11
If the
malfunction is
removed?
No
Yes Y
End
42
No N
Check connection
wire of indoor and
outdoor unit with
circuit diagram
Connection
correct?
No
N
No
Check connection
wire of indoor and
outdoor unit with
circuit diagram
Does the unit operate
normally?
Yes