Thermostat has power but will not turn on cooling when room is above setpoint

Warning: Turn off power to indoor and outdoor units before wiring work.

• Step 1 – Verify settings:
  • Ensure the thermostat is set to Cool mode and the setpoint is below room temperature.
• Step 2 – Inspect Y wiring:
  • Check that the Y/Y1 wire is secure at both thermostat and furnace/air handler board.
  • Inspect any float switches or safety devices in series with Y for tripping.
• Step 3 – Test system response:
  • At the furnace board, jumper R to Y; if the outdoor unit starts, the thermostat or wiring is at fault.
• Step 4 – Measure Y output:
  • With a cool call active, measure voltage between Y and C at the thermostat; should be ~24VAC.
  • If no voltage, the cooling relay is likely defective.
• Step 5 – Replace thermostat if Y output is bad:
  • Replace the thermostat if it cannot energize Y with a cool call.