E1 displayed on indoor unit, system does not run or stops shortly after starting

Safety: Shut off power at both the indoor air handler and outdoor condenser disconnects before opening any panels.

• Verify wiring connections: Remove the electrical covers on both indoor and outdoor Fraser‑Johnston units. Compare the low-voltage/communication wiring to the unit wiring diagram. Ensure the same terminal labels (e.g., 1–2–3 or S1–S2–S3) match end-to-end and that polarity is not reversed.
• Tighten terminals: Check all screw terminals for the communication cable and tighten. Loose screws can cause intermittent E1 faults.
• Inspect cable: Follow the communication cable run. Look for cuts, rodent damage, or splices. Repair or replace damaged cable with the same gauge and type (typically shielded 18 AWG for Fraser‑Johnston communicating systems).
• Check outdoor board LEDs: Restore power and observe the outdoor control board status LED (if equipped). A dead board (no LED) with correct line voltage indicates a failed outdoor control board.
• Reset system: After corrections, power down both units for 5 minutes, then power up outdoor first, then indoor. Clear E1 and test operation.

Professional help: If communication wiring checks good but E1 remains, the outdoor or indoor control board may need replacement and configuration by a technician.