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BS Unit Valve Malfunction During Simultaneous Cooling/Heating Operation

Likely causes

BS unit valve coil open circuit or resistance failure — valve switching impossible

Check: Measure BS unit valve coil resistance: normal 20–60Ω → check for open circuit (infinity) or short (0Ω) → check LED indicator (cooling=red, heating=blue)

What to do: Replace faulty coil → confirm LED color switching after replacement → retry simultaneous cooling/heating operation

BS unit PCB control output failure — coil normal but no signal output

Check: After confirming normal coil resistance → measure PCB output pin voltage (normal DC 12–24V signal) → if no signal confirmed, PCB failure diagnosis

What to do: Replace BS unit PCB → re-confirm address settings → verify normal LED display, then test simultaneous cooling/heating operation

BS unit refrigerant pipe valve seat wear — incomplete cooling/heating separation

Check: Measure gas pipe temperature at cooling-mode indoor unit → verify gas pipe low temperature during cooling (normal = low pressure gas during cooling) → check for reverse refrigerant flow symptoms

What to do: Recover refrigerant → replace BS unit valve assembly → nitrogen leak test after reassembly → re-verify simultaneous cooling/heating operation

Field tip

Check BS unit LED to instantly identify valve status: cooling=red, heating=blue — if LED state doesn't match actual operation mode, suspect coil or PCB failure.

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