I have an ac and heat system with an aprilaire 6202 zone conrol. The heat and ac work fine but the zone control does not seem to direct the flow to up or down stairs correctly. The system is directing air mostly to the upstairs. The flow does not change whether I use the up or down stairs thermostate.
The fuses are good and the green light is flashing in the control unit. What is wrong.

Its not uncommon for a zone damper to go bad or stick. You will have to check for 24v at the damper motors to see if one is stuck open or closed or just getting in a bind in the half way position.