How to Fix / Troubleshooting

Safety: Use extreme caution around high voltage. Turn off the breaker before opening the outdoor unit.

1. Check breaker and disconnect: Verify the AC breaker in the panel is ON. At the outdoor disconnect, ensure the pull-out or switch is fully inserted/on.
2. Listen for contactor click: With thermostat calling for cooling, stand near the condenser. If you do not hear a click, the contactor may not be energizing.
3. Inspect low-voltage wires: Remove the control panel cover and check the small thermostat wires on the contactor coil. Tighten loose connections and repair any damaged cable.
4. Replace contactor if coil is open: With power off, a technician can test the contactor coil resistance. If open, replace with the correct Lennox contactor.

Note: If the breaker trips immediately when reset, do not keep resetting; call a professional to locate the short.

Outdoor Lennox air conditioner unit will not turn on at all; indoor blower runs and thermostat appears normal but condenser is silent.

Possible Causes