E8
Nest
Compressor Call Circuit Fault (Y1)
Nest thermostat shows E8 and reports a problem with the Y1 wire or cooling system
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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
Loose or disconnected Y1 wire at Nest base, Loose Y1 wire at furnace/air handler control board, Blown low‑voltage fuse due to short on Y1 to C, Shorted thermostat cable to outdoor condenser
How to Fix / Troubleshooting
Safety: Turn off power to both the indoor unit and outdoor condenser at their breakers before inspecting wiring.
- Check Y1 at Nest: Remove the Nest display and verify the Y1 wire is fully inserted and clamped. Re‑strip if necessary.
- Inspect furnace board: At the indoor unit, confirm the thermostat Y1 conductor is firmly attached to the Y or Y1 terminal on the control board.
- Check outdoor unit connections: At the condenser, inspect the low‑voltage cable where it enters the unit. Ensure the two control wires (usually Y and C) are intact and firmly connected, with no insulation damage.
- Fuse check: Inspect the low‑voltage fuse on the furnace control board. Replace if blown with the same rating and investigate for shorts if it blows again.
- Cable inspection: Follow the thermostat cable path between indoor and outdoor units, looking for crushed or chewed sections. Replace damaged cable.
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Repair Difficulty
Medium
3/5
Required Part
Y1 Cooling Call Wire / Low‑Voltage Cable to Condenser
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