Lennox
Intermittent Outdoor Unit Communication
Thermostat shows 'Outdoor unit offline' but cooling still works intermittently.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Marginal ABCD wiring connection at outdoor unit, Moisture or corrosion on outdoor low-voltage terminals, Outdoor control board communication circuit intermittently failing, Electrical noise or interference on communication bus
How to Fix / Troubleshooting
Safety warning: Turn off power at the outdoor disconnect and indoor breaker before opening outdoor panels.
- 1. Inspect outdoor low-voltage terminals:
- Clean any corrosion and tighten ABCD or R/C/Y/O/B connections.
- 2. Check cable entry:
- Ensure the cable is properly strain-relieved and not rubbing on sharp metal.
- 3. Seal against moisture:
- Use appropriate grommets or sealant to prevent water ingress into the control compartment.
- 4. If communication drops continue:
- A Lennox technician should evaluate the outdoor control board and replace if necessary.
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Repair Difficulty
Hard
4/5
Required Part
Lennox Outdoor Unit Control Board
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