Outdoor unit does not start, indoor unit shows E1 or flashes timer LED in E1 pattern

Safety first: Turn off power at both indoor and outdoor disconnects before opening any electrical covers. Use a meter only if you are trained to do so.

• Check interconnecting cable: Locate the terminal block in both indoor and outdoor units. Verify that the communication terminals (often labeled 1-2-3 or S1-S2-S3) are wired identically at both ends and that screws are tight.
• Inspect cable condition: Follow the cable run between units. Look for cuts, rodent damage, crushed sections, or signs of water ingress. Replace the cable if any damage is found.
• Verify polarity: Ensure that terminal 1 on the indoor is connected to terminal 1 on the outdoor, 2 to 2, etc. Reversed wires can cause E1.
• Check for multiple systems: If several Fujitsu systems share a conduit, confirm that no cables are cross-connected between different outdoor units.
• Power cycle: After correcting wiring, turn off both indoor and outdoor power for 5 minutes, then restore power and test.
• Board diagnosis: If wiring is correct and E1 persists, the fault may be in the indoor or outdoor PCB communication circuit. This requires a technician with Fujitsu diagnostic tools to confirm and replace the correct board.