Hello,
I have had the same Issues in the past. what Frankie said is most probably the case. but if not here are a few things I have learned over the years which helps alot with maint skimmers.
first try to blow into the air line (after checkign to be sure its instaled correctly) and once it draws air, place it in RO/DI water, so it pulls RO/DI water through the venturi to clean it out, I do this weekly to maintain top performance. second is to simply turn it on and let all the water inside to pure out, so if anything (detritus) blocking the intake it can come out.
if the venturi is stock, then you need to wash it in vineager, and performing the ro/DO thing above will ensure it wont get clogged again. lastly, check how low is the pump under water. you may have to bring the pump closer to surface of water for it to pull air in.
good luck with the new skimmer