WiremanWireman · Mini-split error or won’t start: troubleshooting for electricians · 2023 NEC ·
Mini-split error or won’t start
Power at each unit, the communication wiring, and what each kind of error code means.
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How it works
A ductless mini-split has an indoor unit and an outdoor unit that talk over a communication wire. On many systems the outdoor unit gets power from its own breaker and feeds the indoor unit through the same interconnect cable that carries the signal; others power each unit separately. The outdoor unit uses an inverter board to drive the compressor, and its DC capacitors can hold a dangerous charge for minutes after power is off. Error codes differ by brand, but they fall into a few groups the manual will list.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What is the system doing?
- Indoor unit dead, no lightsTest: Check power at the outdoor unitExpect: The nameplate voltage: usually about 240 V (or 208 V), or 120 V on smaller units.
- No voltage at the outdoor unitNo power to the system
- Voltage presentTest: Check power at the indoor unitExpect: The same supply voltage you read outdoors.
- Power at the indoor terminals, unit deadIndoor board or its fuse
- No power at the indoor terminalsDamaged interconnect cable
- Showing an error code or blinking lightLook up the code in the manual or on the label inside the cover. What kind of fault is it?
- CommunicationTest: Check the interconnect wiringExpect: Matching terminals at both ends, tight connections, and continuity on every conductor with no shorts between them.
- Terminals swapped or looseMiswired or loose interconnect
- Open or damaged conductorDamaged interconnect cable
- Wiring tests goodIndoor or outdoor board not communicating
- Sensor or thermistorA failed temperature sensor
- High pressure, high temperature or overcurrentThe unit shut itself down for protection
- Inverter, compressor drive or IPMInverter or compressor drive fault
- Fan motorIndoor or outdoor fan motor fault
- CommunicationTest: Check the interconnect wiringExpect: Matching terminals at both ends, tight connections, and continuity on every conductor with no shorts between them.
- Indoor runs, outdoor never startsTest: Check the interconnect wiringExpect: Matching terminals at both ends, tight connections, and continuity on every conductor with no shorts between them.
- Terminals swapped or looseMiswired or loose interconnect
- Open or damaged conductorDamaged interconnect cable
- Wiring tests goodIndoor or outdoor board not communicating
- Doesn’t respond to the remoteRemote or receiver
- Indoor unit dead, no lightsTest: Check power at the outdoor unitExpect: The nameplate voltage: usually about 240 V (or 208 V), or 120 V on smaller units.