Heat pump blows cold on heat (or warm on cool): O/B setting
The O/B terminal drives the reversing valve. Most brands energize it in cooling (O); Rheem and Ruud typically energize it in heating (B). A wrong O/B setting reverses the modes. Check the equipment diagram, not wire color.
Cross-checked ~20 min easyBrands: All
Before you start
- Low-voltage only
- Refrigerant-side reversing-valve replacement is refer-out (EPA 608)
Diagnostic steps
Unlock all 4 steps with expected values
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