Goodman MSG-12CRN1N Service Instructions Manual page 21

TROUBLESHOOTING
Diagnostic Chart
If, after energizing the unit, no indicator is lit and the unit cannot be operated, see the following chart.
Be sure all the wires (including power wires and connection wires)
Check for AC (208-230V) power supply outputs to
Check if AC (208-230V) exists at primary coil
of transformer (18K & 24K models only)
Check if AC 12V and AC 35V (+5%) exist at secondary coil
of transformer in the outdoor control board
Take off the secondary plug of transformer, and then check if AC
12V and AC 35V (+5%) exist at secondary coil of transformer
Yes
(for 12k Models)
are OK
Yes
outdoor control board
Yes
Yes
No
No
Transformer is defective
No
No
Yes
Check if DC 35V exists between
2 & 3 on the indoor terminal
and DC 12V between 3 & 4
Yes
Check if DC 35V exists
at CN6 and 12V
at CN3
Yes
Uncertain problem on
Indoor control board.
Change it & check again.
Install good ones
Outdoor
control board
is Defective
Outdoor
control board
is Defective
No
Indoor
control board
No
is Defective
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