E19
American Standard
Reversing Valve (O/B) Control Fault
Thermostat displays E19 and heat pump reversing valve does not operate correctly
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Misconfigured O/B setting (energize in heat vs. cool), Open or shorted O/B wire, Failed O/B output relay, Reversing valve coil failure on outdoor unit
How to Fix / Troubleshooting
Safety: Turn off power to indoor and outdoor units at the breakers before working on O/B wiring.
- Verify system type: In installer settings, confirm the system is set as a heat pump and that the O/B setting matches the American Standard heat pump requirement (typically O = energized in cooling).
- Check O/B wiring: Inspect the O/B wire at the thermostat, furnace/air handler, and outdoor unit. Tighten loose connections and repair any damaged cable.
- Test operation: With power restored, command cooling and then heating. Listen for the reversing valve solenoid click at the outdoor unit. If the thermostat energizes O/B but the valve does not move, the outdoor coil may be faulty.
Resolution: If wiring and outdoor coil are good but E19 persists, the thermostat’s O/B relay may be defective.
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Repair Difficulty
Hard
4/5
Required Part
American Standard thermostat O/B output or heat pump reversing valve coil
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