I have a Lennox furnace in my attic with heat pump? Outside. My unit seems to be running fine (in fact 24/7) but I'm getting no cool air through the registers. What should I do? I have turned the unit and my downstairs unit is attempting to cool the whole house.

If the condenser and compressor are working, could be a broken zone valve if so equipped, clogged filter, collapsed duct or other items.