Error code
21 Unit-number or refrigerant-circuit address setting fault
Applies to 3 models
ASYG09KMCB, ASYG12KMCB, ASYG14KMCB
What this means
Incorrect unit number or refrigerant-circuit address in Simultaneous Multi systems.
When to call a technician
This fault involves refrigerant, pressure, or electrical work that must be handled by a certified technician under EU F-gas rules. Do not attempt to open the refrigerant circuit, access mains wiring, or adjust pressure components yourself. Contact a qualified installer or servicer for this one.
See the official Fujitsu manualA deep link to the manufacturer's own PDF for full technical detail. We link to manuals, we never host them.