u4
Moderate
Daikin · Mini-Splits & Ductless Systems
Communication Error Between Indoor and Outdoor Units
Quick Answer
Error code U4 on your Daikin Mini-Splits & Ductless Systems means: Communication Error Between Indoor and Outdoor Units. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Check all interconnecting wire connections at both the indoor and outdoor unit terminal blocks
2
Test each conductor in the communication cable for continuity end to end
3
Verify the correct wire is connected to the correct terminal at both ends per the wiring diagram
4
Inspect the cable run for physical damage, especially where it passes through walls or is exposed outdoors
5
If the wiring tests good, a licensed HVAC technician should diagnose the indoor and outdoor PCBs
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Interconnecting communication cable
Indoor PCB
Outdoor PCB
Terminal block connectors
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