Thermostat is on but does not call for cooling when room is warm

Safety first: Turn off power to indoor and outdoor units at the breakers before working on wiring.

Steps to troubleshoot:

• 1. Verify mode and setpoint: Set the Emerson thermostat to Cool mode and lower the setpoint several degrees below room temperature.
• 2. Check schedule and holds: Temporarily disable schedules and use a manual cool hold to ensure the thermostat is allowed to call for cooling.
• 3. Inspect Y/Y1 wiring: Remove the thermostat and confirm the Y/Y1 wire is secure. At the furnace/air handler board, verify the same conductor is attached to Y.
• 4. Confirm configuration: In installer setup, ensure cooling is enabled and the number of cooling stages matches your equipment.
• 5. Test with jumper (advanced): With thermostat removed and power on, briefly jumper R to Y at the furnace board. If the outdoor unit starts, the thermostat is not sending a cooling call and may be misconfigured or defective.

When to call a professional: If the outdoor unit does not start even with a direct R–Y jumper, an HVAC technician should inspect the contactor, control board, and safety circuits.