Air horn not working

Find the solenoid and have someone press the horn button to see if it clicks. If it does you know it is getting power. Then go up on top and again press and hold horn button. Can you hear any air. If not either the solenoid is not working or something has built nests in your air horn. Remove the horn bell and look through. On my coach, both bells had insect nests. Fixed by poking the nests out. I now "exercise" my air horn on every trip to make sure the solenoid is still working and that no nest builders have been busy.