Lennox Air Conditioner Error Code E345

The 'O' relay on the outdoor board has failed - either the pilot relay contacts did not close, the relay coil did not energize, or the confirmation circuit is not sensing properly.

First step from the service manual

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

• 1Power loss for two electrical cycles (33-40 milliseconds)…
• 10Option 2 safety device switch opens.
• 11Compressor temperature sensor wires have shorted together.
• 14Control is in TEST mode; does not indicate a problem.
• 15Mode jumper is not in place on the TSC5 two-speed control.
• 2Input indication
• 3Unsteady thermostat input
• 4Pressure switch opens after compressor has run for less…