I have one ac unit and two thermostats (one up stairs, one down). Upstairs turns on blower but not ac. Downstairs works fine. Since therms are the same I switched them out and both work downstairs but not upstairs. Ac unit is Amana and thermostats are Lux.

Yellow wire prob or wire prob in general from the t-stat to the air handler or unit (if package unit).

check image glossary for pics (http://www.thermal-medics.com/a-c-image-glossary/)

What type of Zone controller do you have? Sounds like problem's with that. Can you locate the two damper motors? Get model and serial # of Zone Control Panel---Should be near Air Handler--Same with damper motors. I will try to help.