I have two heat pumps one for upstairs and one for main level.Upstairs blower is in attic and main level one is in basement.I can hear then blower and feel air coming out of registers upstairs.Main level can't feel air coming out and it sounds like the fan is stuck or something because I can hear a buzzing sound like the fan is trying to run but is locked up or stuck.My thinking is if the fan is locked up it would trip breaker??

Sometimes a motor will just sit there an make a buzz sound. Turn off power and remove blower door then reach in and feel fan motor. If hot then the motor is probably bad. Next step is to call for service and get it fixed unles you want to do the job yourself.

Check capaitor on motor first,if you don't know much about it. Has it checked. They will bite.