ActronAir Indoor Evaporator Fan Deck 9x7 S 3/4HP ECM is a higher-output ECM deck than the 1/2HP variants, providing greater static pressure capability for ESP Plus and Ultima indoor units with more extensive duct systems or higher-resistance multi-zone configurations. If the fan runs at high speed when only one or two zones are open, the fault is typically the indoor PCB zone load algorithm rather than the fan deck itself -- diagnose the PCB before replacing this assembly. Isolate power at mains before replacement -- live work on fan assemblies is dangerous and must only be performed by a qualified technician.