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

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.