From the Ingersoll Rand manual:

" STARTER FAULT 1SL (2SL)- This will occur if the starter contacts open while the machine is running. It will also occur if the machine is given the stop command and the starter contacts do not open. 1SL refers to the auxiliary circuit on starter contact 1M. 2SL refers to the auxiliary circuit on starter contacts 2M and 1S."

So it's basically an electrical problem with the start contacts.

What is meant by this is the big relays/contactors that switch the main motor on and off.

These relays have auxiliary (small) contacts on them, so the control system can 'see' whether they are open or closed.

So if the controller closes the relay (contactor) but it stays open (according to the auxiliary contact), then this error will occur.

In your case, the problem is with contacts 2M and/or 1S.

What is often the case with older compressors, is that this auxiliary contact is simply bad. So it's a false alarm actually. Depending on the model, you will need to completely replace the relay or you can replace only the auxiliary contact.

If you are not familiar with electrical systems, please do not attempt to fix it yourself but call in an electrician!

Please see the pictures below for more info!

Good luck!

Cas