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Error code reference
Lennox Air Conditioner Error Code 15
Mode jumper is not in place on the TSC5 two-speed control.
SourceLennox HS21 Series - Service Manual: Air Conditioner Unitsp. 12
Diagnostic procedure
The full 15 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
Make sure jumper is placed securely across the selected set of pins for the appropriate mode of operation.
SourceLennox HS21 Series - Service Manual: Air Conditioner Unitsp. 12
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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