Compressor Oil Filter High Differential Pressure Warning
What does SULLAIR-E080 mean?
The SULLAIR-E080 (Sullair WS Controller) diesel fault code means: Compressor Oil Filter High Differential Pressure Warning. This is a moderate severity code.
Common Symptoms
- WS Controller LCD displays E080 or 'OIL FILTER RESTRICTION' on the side panel
- Yellow warning light illuminates on the control panel but machine continues to run
- Compressor may show slightly elevated oil temperature alongside this fault
- Machine completes current cycle but annunciates the fault at shutdown on some firmware versions
- Audible alarm beep sequence accompanies the fault display on WS Controller units
- Fault log in the WS Controller records timestamp and hours at time of trigger
- No immediate shutdown occurs, but fault persists across restart until filter is serviced
Probable Causes (Ranked by Likelihood)
- Oil filter element at or beyond service interval, loaded with contaminants Very Likely
- Extended operation in dusty or dirty environments accelerating filter loading Very Likely
- Wrong viscosity or non-Sullair-approved fluid causing higher cold differential pressure at startup Likely
- Cold ambient temperature causing high fluid viscosity and elevated differential at startup, not a true blockage Likely
- Differential pressure switch or sensor fault giving a false high-restriction reading Possible
- Sump contamination from water ingestion or coolant intrusion pushing debris into filter Possible
- Incorrect replacement filter (wrong micron rating or bypass valve spec) installed at last service Less Likely
Step-by-Step Diagnostic Procedure
Check the WS Controller LCD for active fault history. Navigate to the fault log menu and note the machine hours at the E080 trigger. Compare to your last recorded oil and filter change hours. If you are at or past the 1,000-hour or annual service interval, the filter is the first suspect.
Inspect the compressor oil filter element visually. On most Sullair 185 through 750 towable units the oil filter is on the fluid sump assembly on the compressor end. Look for external debris, damage to the housing, or oil seeping past the gasket, which can indicate bypass conditions.
Check the compressor fluid level in the sight glass on the sump tank. Low fluid level can cause aeration and false differential pressure spikes. Fluid should read in the middle of the sight glass at operating temperature with the machine unloaded.
If ambient temperature is below 40 degrees F, allow the machine to warm up fully at idle for 5 to 10 minutes, then note whether E080 clears on its own. Cold Sullair fluid AW 46 or SRF 4000 series has significantly higher viscosity at startup and can trip the differential switch before the fluid warms.
Locate the oil filter differential pressure switch. On WS Controller units it is typically a two-wire normally-open switch that closes when pressure differential exceeds specification, around 25 PSI differential. With the machine off and lockout applied, unplug the switch connector and use a multimeter set to continuity or resistance. A good switch reads open circuit when the filter is cold and unpressurized. A switch stuck closed when the machine is off and at ambient temperature points to a failed switch, not a clogged filter.
If the switch checks out, replace the compressor oil filter element and perform a full fluid service using Sullair-approved SRF 4000 or equivalent spec fluid. Reset the fault via the WS Controller maintenance reset menu after service. Restart and run to operating temperature, then verify E080 does not return.
If E080 returns immediately after a fresh filter and fluid service at normal operating temperature, pull a fluid sample for analysis. Contamination with water or metal particles indicates an internal issue requiring advanced inspection. At that point contact a Sullair service tech, as further operation risks screw element damage.
Frequently Asked Questions
What does Sullair code E080 mean?
E080 means the WS Controller has detected a high pressure differential across the compressor oil filter. In plain terms, the filter element is restricted enough that the controller is warning you it needs to be replaced. The machine can still run but you are pushing dirty fluid through or approaching bypass, which means unfiltered oil could reach the screw element if you ignore it.
Can the compressor still run with E080 active?
Yes, in most cases the machine stays running and does not shut down on E080 alone. It is a warning, not a shutdown code. That said, you should not ignore it. If the filter goes into full bypass, the screw element runs on unfiltered fluid and wear accelerates fast. Plan to service it before the next full day of use.
How much does it cost to fix E080?
If it is just an overdue filter, a DIY filter and fluid service runs roughly $40 to $120 in parts depending on the unit size. A rental yard or Sullair dealer doing a full fluid change with inspection will typically charge $150 to $400. If the differential pressure switch itself has failed, add $30 to $80 for the switch part plus labor.
Will E080 go away on its own after I change the filter?
Yes, once you replace the filter and reset the fault through the WS Controller maintenance menu, E080 should clear. If it comes back immediately after a fresh filter at normal operating temperature, you have either a faulty differential pressure switch, contaminated fluid, or a deeper fluid system problem that needs a Sullair tech to evaluate.