Why won't my Sullair compressor unload?
Short answer: Compressor did not unload. If your Sullair Touch Screen (STS) is showing Failed to Unload, the controller has logged a specific, documented condition. This page covers what it means, what causes it, what you can safely fix yourself, and when — and why — it takes a technician.
What exactly is the machine telling you?
The compressor failed to unload when commanded. The manual points to the inlet valve and its controls.
Which machines show this?
current-generation Sullair stationary rotary screw compressors — the LS-series and related packages built from the late 2010s onward — fitted with the 10-inch Sullair Touch Screen (STS) controller. The STS spells out problems as plain-English named faults and warnings ('High Temperature 1', 'Failed to Unload', 'Replace I/O Battery') rather than bare code numbers, and pairs them with live readings and a Recommended Service screen that tracks filter and separator hours. Warnings keep the machine running; faults shut it down until reset. Practical tip: before clearing anything, photograph the fault screen and the Recommended Service page — the service-hour counters usually point straight at the consumable that caused the trip.
What causes it?
- Inlet valve or its controls not closing the machine off when commanded — the manual's pointer
- Leaking or disconnected control tubing around the inlet valve
Can you fix it yourself?
Partly — one stop/restart, a visual check of control tubing, and notes on when it happens (low demand, shutdown) are the in-house scope.
Step by step — what to try, in order:
- Stop the machine and restart once to see if it unloads normally
- Check for obvious air leaks or disconnected control tubing around the inlet valve (visual only)
- Record when the fault occurs (at low demand, at shutdown) for the technician
When do you need a technician — and why?
Inlet valve and unloading-control inspection is service work on the machine's control air circuit — the components live under pressure in operation.
If it does come to a service call and you're in Nashville, TN or Birmingham, AL, we maintain independently compiled lists of local companies that service industrial air compressors — real businesses with verified contact information, none of whom paid to be listed.
Related questions
What does Failed to Unload mean on a Sullair Touch Screen (STS)?
Compressor did not unload. The compressor failed to unload when commanded. The manual points to the inlet valve and its controls.
Can I fix Failed to Unload on a Sullair Touch Screen (STS) myself?
Partly — one stop/restart, a visual check of control tubing, and notes on when it happens (low demand, shutdown) are the in-house scope.
When does Failed to Unload on a Sullair Touch Screen (STS) need a technician?
Inlet valve and unloading-control inspection is service work on the machine's control air circuit — the components live under pressure in operation. Call service to inspect the inlet valve and unloading controls if the fault repeats.
Verified against service documentation: Sullair Touch Screen (STS) documentation for Failed to Unload (sullair.com)