What does E1 mean?
Communication signal between indoor and outdoor unit has failed or is interrupted.
Common causes
- Damaged communication wire between units
- Incorrect wiring polarity
- Failed indoor or outdoor PCB
- Power supply issue at one unit
- Loose terminal block connections
Diagnostic & testing steps
- 1. Check communication wire voltage: should read 12-24VDC pulsing
- 2. Verify wire terminals are tight and correct (S1, S2, S3 or similar)
- 3. Test wire continuity from indoor to outdoor unit
- 4. Check for wire damage from stapling, pinching, or rodent damage
- 5. Try replacing communication wire if damaged
Tools required
- Multimeter
- Multimeter with DC voltage range
OEM parts & part numbers
Communication Wire, Indoor PCB, Outdoor PCB
Part numbers: KRP980B2, 5003521, 5003522
Safety warning
⚠️ Disconnect power before accessing PCB boards.
Try DiagBuddy AI free — instant 30-second diagnostics for technicians.