Hi,

There is probably some kind of feedback from the inverter drive to the compressor control panel.

Is it a digital control panel (if it has a vsd drive, probably) - does it communicate with the new drive? Or can you only set speed manually?

If all this is OK - can you press 'load' on the controller and does it indicate it switches (or runs) loaded?

It could be a mechanical problem with the inlet valve, or with the control pneumatics (control line, loading solenoid, etc).

Start with the loading solenoid and see if it gets power (multimeter) - if not, check if you can trace it back to the control panel.

If it does get power, make sure it actually opens and control air is supplied to the inlet valve.

Please check these first and report back :)

All the best,

Cas