Thank you for your question. With a dual zone system, one unit cannot heat while the second indoor unit cools or vice versa. This is because the condenser, which runs each air handler, runs one way for cooling and another way for heating. However, the air handler can heat or cool each zone at different temperatures. For instance when you are heating your home, you can set one zone at 5 degrees warmer than the other zone. Or when cooling, you can have one zone set at a higher setting than the other zone. For more assistance, please give us a call.