Thermostat displays E3 and will not start cooling; AC condenser does not turn on.

Safety first: Turn off power to both the furnace/air handler and outdoor condenser at the breaker.

• Check Y1 at thermostat: Remove the Wyze display and verify the Y1 (often yellow) wire is fully inserted and clamped in the Y1 terminal. Re-strip the wire to expose clean copper if needed.
• Inspect Y1 at furnace/air handler: At the control board, confirm the same colored wire is firmly attached to the Y terminal. Tighten the screw and ensure no stray strands are touching adjacent terminals.
• Verify adapter wiring: If using a Wyze C-Wire Adapter, confirm the Y wire from the thermostat is in the correct adapter port and the adapter’s Y lead is on the Y terminal at the control board.
• Continuity test (advanced): With power off, disconnect the Y wire at both ends and use a multimeter in continuity mode to test the conductor. No beep or infinite resistance indicates a break in the cable that may require running a new thermostat cable.
• Restore power and test cooling: Reconnect everything, restore power, set the thermostat to Cool and a temperature well below room temp. The E3 code should clear and the outdoor unit should start after any built-in delay.