Thermostat displays a warning that the AC/heat pump is not responding when a cool call is made

Safety: Turn off power to both the furnace/air handler and outdoor unit at the breakers before working on wiring.

• Step 1 – Verify ecobee configuration: In Installation Settings > Equipment, confirm that cooling is enabled and assigned to Y1.
• Step 2 – Inspect Y wire at thermostat: Remove the ecobee and ensure the Y1 wire is fully seated and clamped.
• Step 3 – Inspect Y wire at furnace/air handler: Open the panel and verify the Y wire is connected to the Y terminal on the control board and that the cable to the outdoor unit is connected to Y and C.
• Step 4 – Check fuse and 24V: Inspect the low-voltage fuse on the furnace board. With power on, measure 24 VAC between R and C, and between Y and C when cooling is called. If Y is not energized, the board or thermostat wiring is suspect.
• Step 5 – Test outdoor contactor: At the outdoor unit, with power off, inspect the contactor coil connections. With power on and a cooling call, measure 24 VAC at the contactor coil. If voltage is present but the contactor does not pull in, replace the contactor.