Outdoor unit does not start, indoor fan may run, display shows E1

Safety first: Switch OFF the breaker for the air conditioner before touching any wiring at the indoor or outdoor unit.

Steps to check:

• Power reset: Turn off the breaker for 5 minutes, then turn it back on and try operating the unit. If E1 reappears, continue with wiring checks.
• Verify terminal wiring: Remove the indoor unit terminal cover. Confirm that terminals 1–2–3 (or L–N–S depending on model) match exactly with the outdoor unit terminals (1 to 1, 2 to 2, 3 to 3). Correct any mis‑wiring.
• Check cable condition: Inspect the interconnecting cable between indoor and outdoor units along its entire run. Look for rodent damage, crushed sections, or signs of water ingress. Replace the cable if insulation is damaged.
• Tighten screws: Loose terminal screws can cause intermittent communication. Tighten all terminal screws firmly but without over‑torquing.
• Measure voltage (qualified persons only): With power ON, a trained person can verify that the communication line has the specified voltage (often DC 12–30 V depending on model). If no voltage is present, the indoor or outdoor PCB may be defective.

If wiring is correct and intact but E1 persists: One of the control boards is likely faulty. Contact a Hitachi service technician for PCB diagnostics and replacement.