What it means
Pressure drop across the compressor fluid filter is high while the machine is running.
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
- Fluid filter clogged or restricted
- Low ambient temperature causing high fluid viscosity
- Differential-pressure sensor, wiring or tubing problem
Operator-safe first checks
- Record ambient temperature and whether the condition clears as the machine warms.
- Do not bypass the fluid filter or pressure sensing circuit.
Trained maintenance / service checks
- Replace the fluid filter when confirmed restricted.
- For cold environments, verify whether the package requires a sump heater.
- If the condition remains, inspect the sensor, wiring and sensing tubing.
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: 31.