Welcome to the Forum!

Air is going to be caused by a suction side issue - either a leaking line pulling air in or a problem at the skimmer, like the water level too low or the skimmer 'door' (weir) stuck in the up position.

Do you see air in the pump basket?

Give us enough info and a little time and we ought be able to help you determine the cause and then we'll help you firure out the best way to address the issue.