Thermostat is on but will not turn on cooling when temperature is set lower than room temperature

Safety first: Turn off power to the air handler and outdoor unit before working on wiring.

• Step 1 – Verify mode and setpoint: Ensure the thermostat is in Cool or Auto mode and the setpoint is at least 2–3°F below the room temperature.
• Step 2 – Check delay timers: Many iComfort thermostats have compressor protection delays (e.g., 5 minutes). Wait at least 5–10 minutes after changing the setpoint.
• Step 3 – Inspect Y wiring: Remove the thermostat and verify that the Y/Y1 wire is secure and not damaged.
• Step 4 – Test outdoor unit response: At the air handler or furnace board, temporarily jumper R to Y. If the outdoor unit starts, the thermostat or its wiring is at fault. If not, the issue is with the outdoor unit or control board.
• Step 5 – Confirm configuration: In installer setup, verify that cooling is enabled and the correct number of stages is configured.
• Step 6 – Replace thermostat/interface: If manual jumpering works but the thermostat will not energize Y, the thermostat or interface module cooling output is likely defective and should be replaced.