Fault Code Lookup

HVAC Sales Master

Open Inducer Limit switch

This code typically points to

Open inducer limit switch

Next checks to confirm

Check inducer limit continuity
Public abnormal-condition text also points to variable-speed draft inducer troubleshooting manual

Escalation

Heating interrupted

Reset behavior

Device must cool/clear.

Urgent

Fix now

⚠ Cross-generation conflict

Code 9 means completely different things across Trane/American Standard legacy platforms. On UD2/DD2 and UC1/DC1, it's an ignitor/grounding fault. On AUY/TUY and AUH2/TUH2, it's an open inducer limit — totally different diagnostic path. Your model prefix determines which it is.

Source

Trane 18-CD20D3-21 Installer's Guide, p.35-36

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