Compressor Operation — Start, Load/Unload & Stop – South-Tek Systems

Applies to: STS Series (5–100HP) · STSH Series · STSD · STSP · STSP2

Before Every Start

⚠ Warning Never operate the compressor if any mechanical, hydraulic, or electrical component is known to be defective. Resolve all faults before starting.

Check oil level at the sight glass with the compressor stopped. Oil should sit in the middle-to-MAX band of the sight glass. Do not start if oil is at or below the minimum mark.
Confirm all cabinet doors are closed and latched.
Verify the AirMASTER FORM controller shows no active faults.
Confirm the air outlet valve is open.

[ IMAGE — FIG-01: Oil sight glass showing Min. / Max. level marks ]

Starting the Compressor

Open the air outlet valve.
Energize the compressor at the main disconnect.
Press the START button on the AirMASTER FORM controller panel.
The compressor will start and begin loading after the configured delay time expires.

ℹ Note On units rated 188 PSI and above, the control air operating pressure at the suction control valve is preset to 6 bar (87 psi) by a pressure regulator and must not be adjusted. Verify this setting while the compressor is running.

During Operation

During normal operation the compressor cycles automatically between load and unload states based on system pressure:

Load: The compressor is compressing air and supplying the system. The suction control valve is open.
Unload: System pressure has reached the upper setpoint. The suction control valve closes and the compressor runs unloaded. If system pressure does not drop to the lower setpoint within the idle timer period, the compressor stops automatically.
Auto-restart: When pressure drops to the lower setpoint, the compressor restarts automatically and returns to load.

⚠ Warning — Automatic Operation If the automatic restart parameter is enabled, the compressor will restart without operator input after a power interruption. Confirm this parameter's state before performing any maintenance. It is disabled in default factory settings.

Routine Checks During Operation

Monitor the AirMASTER FORM display regularly for temperature, pressure, maintenance reminders, and fault alerts.
Periodically verify the scavenge line check valve has oil flowing — this confirms the scavenge line is functioning.
Keep all cabinet doors closed at all times during operation. Never touch internal components or piping while the unit is running.

Checking Oil Level During a Run

Press the STOP button and wait for the compressor to fully stop.
Wait for the oil to drain back (at least 20–25 minutes).
Check the sight glass — oil should sit in the middle-to-MAX band.
If oil is low, press Emergency Stop, close the outlet valve, discharge all compressed air from the system, then add oil per the oil filling procedure.
Always investigate the cause of oil loss before returning the unit to service.

Stopping the Compressor

ℹ Note Under normal conditions, always stop using the STOP button — never the Emergency Stop button.

Press the STOP button on the control panel.
The compressor will run unloaded for the configured unload time, then stop.
Close the air outlet valve.
Discharge pressure in the pipes between the air tank and the outlet valve using the manual drain valve or by pressing the test button on automatic drain valves.

Emergency Stop

In an emergency, press the Emergency Stop button to stop the compressor immediately. This creates an emergency stop fault condition. To recover:

Resolve the condition that required the emergency stop.
Unlock the Emergency Stop button by rotating it.
Press and hold the RESET button on the AirMASTER FORM briefly to clear the fault.
Restart normally.

Fault Recovery

If a fault causes the compressor to stop during operation, the fault information is displayed on the AirMASTER FORM controller screen. Resolve the underlying issue, reset the fault on the controller, then restart the compressor and monitor its operation.

For fault code reference, see the Troubleshooting Guide article.

Need help? South-Tek Systems Service — Phone: (910) 415-1880 · Open a support ticket at support@southteksystems911.zendesk.com or through the Help Center.