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Error code reference
Trane Furnace Error Code 3 Double
2nd stage pressure switch open. Furnace reverts back to 1st stage heating.
SourceTrane Furnace - Service Manual: UD2/DD2 Two-Stage Induced Draftp. 11, 16, 30
Diagnostic procedure
The full 3 Double procedure
Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.
MyPros+ · DiagnosticsStep 1 preview
1
First diagnostic step
Cycle power to furnace and call for 2nd stage heat; verify all wiring to pressure switch is correct per wiring diagram.
SourceTrane Furnace - Service Manual: UD2/DD2 Two-Stage Induced Draftp. 11, 16, 30
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
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Where this code is documented
1 manual in the MyPros+ library documents this code for Trane furnace.
Models covered by the manuals that document this code
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