American Standard Incorrect Wiring / Missing Common (C) Wire

Thermostat does not power up after replacement or new installation

Advertisements

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.

Advertisements

Possible Causes

No C wire connected, R and C reversed or shorted, Using battery-only wiring on a power-hungry smart thermostat, Miswired at furnace control board

How to Fix / Troubleshooting

Safety: Turn off power to the furnace/air handler at the breaker before wiring.

  • Confirm C wire: At the furnace control board, identify the C terminal and ensure a wire from that terminal goes to the thermostat and is connected to C there.
  • Check R wiring: Ensure only the correct R (or Rc/Rh as specified) is connected and not shorted to C or other terminals.
  • Use a C-wire adapter (if needed): If no spare conductor is available, consider an approved C-wire adapter kit compatible with American Standard controls, or have a new cable pulled.

Note: Do not attempt to use ground or other terminals as a substitute for C; this can damage equipment.

Advertisements

Repair Difficulty

Medium 3/5

Required Part

Thermostat low-voltage wiring (R and C conductors)
Check Price on Amazon

We may earn a commission from links on this page.

Advertisements