Carrier 40TGV0131UP Service Manual page 61

[L20 error]
Are wiring connections
to communication lines
U3 and U4 normal?
YES
Is not the multiple same central
control system addresses connected?
NO
Check central controller
(including network adapter) and
indoor P.C. board (MCC-1643).
Defect → Replace
[L30 error]
Do outside devices normally work?
(Outside devices connected with Application
control kit input terminal TB2 : IN1)
YES
Check cause of operation.
[P30 error] (Central controller)
Is group operation carried out?
YES
Is there check code
on follower unit in main
and sub remote controllers?
YES
Check corresponding
indoor unit/outdoor unit.
NO
YES
Correct central control system address.
NO
NO
NO
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Correct wiring connection.
Check outside devices.
Defect → Replace
Check indoor P.C. board (MCC-1643).
Defect → Replace