I have a 2 story home with two separate units with two separate thermostats. The heat and cold air is blowing upstairs, but no heat and cold air blowing downstairs. I turn on the air conditioning on the downstairs level and it comes on outside with no air coming in on the downstairs level. No air blowing through the vents downstairs. Help!

Sounds like you have blower problems
You/someone needs to check the furnace to determine if motor is bad or if something is causing it to not get power

Maybe, u need to close some of thee upstairs vents

Could be something blocking the trunk line or your blower motor is bad... but it could also be a bad fuse or switch... there are fuses on the unit that should be checked by a professional.