The compressor runs at full power even when unloaded because the inlet valve doesn't close properly or the blow-down isn't working. Full power in, zero air out.

What you'll see

During unload, the sump pressure stays at operating pressure (7-8 bar) instead of dropping to the normal 2-2.5 bar. The compressor uses nearly the same energy whether loaded or unloaded. On machines with proper unloading, energy drops to about 25-30% of full load during unload. If your machine uses 100% energy during unload, something is wrong.
Before you assume this is the problem

See all causes of high energy use →

How to diagnose

  1. Check sump pressure during unload

    Watch the sump gauge when the machine unloads. It should drop from operating pressure (7-8 bar) to about 1.7-2.4 bar within a few seconds. If it stays at operating pressure, the inlet valve isn't closing or the blow-down isn't functioning.

    Result: Sump stays high during unload = inlet valve or blow-down problem.

How to fix it

  1. Fix the unloading system

    Check and repair the solenoid valve, inlet valve, and blow-down valve. The compressor must properly unload to save energy. See the Won't Load cause pages for detailed inlet valve and solenoid diagnostics.

  2. Consider VSD or auto-stop

    For variable demand, a VSD (Variable Speed Drive) compressor adjusts motor speed to match demand -- much more efficient than load/unload cycling. For intermittent demand, configure the controller to stop the motor after a timeout period rather than idling at unload indefinitely.

Common mistakes

Running a compressor at full pressure during unload wastes enormous energy. If your compressor spends significant time unloaded, that's where the biggest savings are.

Parts & tools

Solenoid valve, inlet valve, and blow-down valve parts as needed.

Review safety precautions before starting →