R-Pro › Field cases › VRF systems
VRF BS Box (Simultaneous Heat/Cool) Fault
Likely causes
Check BS box solenoid valves + pressure balance
Check: BS box solenoid valves click when modes switch. No operation = coil open or PCB signal fault. Equalizing line leak = some indoors freeze. Communication = BS box has separate comm cable, requires termination resistor. With one indoor cooling and another heating, gas separation (high/low) must work correctly.
What to do: Measure solenoid coil resistance (open = coil bad) + verify PCB signal voltage. Equalizer line leak = trace and repair. Confirm termination resistor on DIP. BS box disassembly only by OEM-certified tech. General tech = diagnose and replace whole BS box assembly or call manufacturer.
BS box = found in Daikin VRV / LG Multi V / Mitsubishi City Multi simultaneous heat-cool systems. Critical in 4-pipe/6-pipe systems. Failure can shut down whole system. Only OEM-certified techs disassemble. General techs = diagnose/replace only.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
Open R-Pro →Related cases
- EEV Stuck — Reduced Cooling/Heating Capacity
- Indoor Unit Drain Pump Malfunction Causing Water Leak
- Indoor Unit Fan Abnormal Noise and Vibration
- Remote Control Reception Failure — Commands Not Transmitted
- Horizontal Indoor Unit Airflow Louver Malfunction
- P/Q Communication Wire Open/Short Circuit — Indoor Unit Communication Error