What it means
Communication between the STS controller and the variable-speed drive has been lost.
This entry is tied to the exact STS message family documented by Sullair. The same words can mean something different on another controller generation, so confirm the displayed message and machine documentation before acting.
Likely causes
- Lost communication with VSD
- VSD control power problem
- Connection or drive-board fault
Operator-safe first checks
- Record whether the drive display is powered and showing its own fault code.
- Do not open the VSD cabinet unless qualified and authorized.
Trained maintenance / service checks
- Check STS-to-VSD connections.
- Verify VSD control power and inspect for drive/board faults using the drive-specific procedure.
Reset or keep running?
Do not use repeated resets as a substitute for diagnosis. If the condition involves electrical power, a motor overload, high pressure, loss of cooling, abnormal temperature, or a safety circuit, correct the underlying problem before returning the compressor to service.
Source confidence
OEM VERIFIED
This message and its troubleshooting direction are traced to the Sullair STS controller troubleshooting guide.
Source: Sullair STS Controller User Manual, part 02250241-178 R01. Referenced manual page: 35.