Schneider Electric Miswiring or Crossed Outputs

Thermostat shows correct temperature but HVAC equipment runs at unexpected times or in wrong mode.

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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

Heating and cooling wires swapped, Reversing valve (O/B) miswired, Shared transformer commons incorrectly tied, Multiple thermostats interfering on same circuit

How to Fix / Troubleshooting

Safety: Turn off power to all affected HVAC equipment before changing wiring.

Steps:

  • Compare thermostat wiring to the Schneider Electric installation diagram and the HVAC equipment terminal labels.
  • Ensure that W (heat), Y (cool), G (fan), and O/B (reversing valve) are connected to the correct corresponding terminals on the equipment.
  • For heat pumps, verify that the O/B terminal is configured correctly in the thermostat (energized in cooling vs heating) and wired to the reversing valve coil.
  • If multiple thermostats share a transformer, confirm that all C (common) wires are correctly tied and that there are no backfeeds between systems.
  • After correcting wiring, test each mode (heat, cool, fan) individually to confirm proper operation.
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Repair Difficulty

Medium 3/5

Required Part

Thermostat Wiring Harness / HVAC Control Board Terminals
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