Carrier 38MBQ Series Service Manual page 32

DIAGNOSIS AND SOLUTION (CONT)
Error Code
Malfunction Decision Conditions
Supposed Causes
Troubleshooting
Check the wiring between the main
PCB and compressor. Is it improperly
wired?
Check the IPM. Is it functioning
Check the outdoor fan and the
outdoor unit ventilation. Is it
functioning properly?
Check the compressor resistance
values. Are they within acceptable
Replace the outdoor main PCB
Table 26—Inverter Compressor Drive Error Diagnosis and Solution (P4)
P4
An abnormal inverter compressor drive is detected by a special detection circuit, including
communication signal detection, voltage detection, compressor rotation speed signal detection and so
on.
S
Wiring mistake
S
IPM malfunction
S
Outdoor fan assembly fault
S
Compressor malfunction
S
Outdoor PCB faulty
No
properly?
Yes
Yes
parameters?
Yes
Ensure proper connection or
Yes
replace the wires and connectors
Replace the IPM board or replace
No
the main PCB
Please refer to "Fan Speed
No
Malfunction"
No Replace the compressor
32