The solenoid works, power is fine, but the control air hose to the inlet valve is plugged with dirt. No air reaches the inlet valve piston.

What you'll see

The compressor runs, the controller shows 'loaded', you can hear the solenoid click -- but the inlet valve doesn't open. The machine stays at unload-running pressure. If you disconnect the control air line at the solenoid outlet, air comes out. But the air never makes it to the inlet valve because the line between them is blocked.
Before you assume this is the problem

Confirm the solenoid is switching and producing control air at its outlet. If no air comes from the solenoid outlet, the problem is the solenoid itself (see: Solenoid Valve Failure) or there's no control air supply at all (see: No Control Air Supply). Also check that the inlet valve itself isn't stuck -- even with good control air, a seized inlet valve won't move (see: Inlet Valve Stuck or Damaged).

Could also be:

See all causes of compressor won't load →

How to diagnose

  1. Check air at solenoid outlet

    Disconnect the control air hose at the solenoid outlet. Press load on the controller. You should feel compressed air coming out. This confirms the solenoid is working and control air supply is available.
    Result: Air at solenoid outlet = solenoid and supply are fine. No air = solenoid or supply problem.

  2. Check air at inlet valve connection

    Now disconnect the same hose at the inlet valve end. Load the compressor. Is air coming through the hose? If yes at the solenoid end but no at the inlet valve end, the hose is plugged somewhere in between.
    Result: No air at inlet valve end = blocked line. Air present = inlet valve is the problem.

  3. Inspect the hose or tubing

    Remove the control air hose completely. Look through it -- is it plugged with dirt, oil sludge, or debris? On older machines these small-diameter hoses can accumulate crud over years. Blow through it with shop air to check.
    Result: Blocked hose = clean or replace it.

How to fix it

  1. Clean or replace the control air line

    Blow out the hose with compressed air from both ends. If it's badly clogged, just replace it -- it's a cheap flexible hose, not worth spending time trying to save. Use the correct diameter replacement hose.

  2. Clean the fittings

    While the hose is off, also clean the fittings on both the solenoid outlet and the inlet valve connection point. Dirt can accumulate in the fittings themselves, not just the hose.

  3. Check for the cause of the blockage

    If the hose was badly clogged with oil sludge, ask yourself why. Old degraded compressor oil creates sludge that can block everything. Check your oil condition and change intervals. If the oil looks like tar, you've been running it too long.

Common mistakes

Don't overlook this simple cause. It's easy to jump to expensive conclusions (bad controller, bad inlet valve) when the problem is just a 2-dollar hose that's plugged with dirt. Always trace the control air path step by step before tearing things apart.

Parts & tools

Replacement flexible control air hose (small diameter, typically 6mm / 1/4 inch). Shop air for blowing out lines. No special tools needed.

Review safety precautions before starting →