Heat rises so the top level of a house will often feel warmer. Under insulation in the attic, drafty windows and lower ceiling height on that level can also contribute to the temperature. If those 3 aren't to blame, can you set the fan setting for the 3rd level to "on" rather than "auto"? (You mention no air flow) If you still don't have any air blowing from the 3rd floor vents you may have a blockage somewhere and be best served by calling in an HVAC service company.
Good luck - hope it's an easy fix!

If there is no air flow to Zone 3, then that zone is not working properly. Is the LED for Zone 3 lit on the HZ322 panel? If it is, then I suspect the damper to Zone 3 is not operating. See if you can find that damper. There may be an indicator on the side showing whether it is open or closed. On some dampers you there is either an indicator light or a mechanical post which indicates if the damper is open or closed. Most likely the damper motor is no longer operating and will need to be replaced or the HZ322 zone panel is not functioning properly.

3 level zones are not easy.

you lack control that is likely part of the problem. If you lack control of a zone system, what does that tell you? (63, 70, 79 is not control.)

A zone system primary function *is* control. Poor design = it won't work. The whole reason for doing it is that it needs to work.

Redesign is how you fix it.

(Note: it's possible other problems exist with this system in addition to zoning issues.)

I service the Katy, Texas area.

If the zone dampers are working correctly, then the problem is the ductwork.

Thanks all, it was a damper problem indeed, it is fixed now