My Infiniti G20 blows cool or warm air on the floor when moving and heat is OFF.?

[wildgeorges@yahooecom]

My infiniti 2000 is running and operating perfectly. But i have a question about the floor air con vent. When the heat is set up high say like 85, and then you press the OFF button, the car will still blow really warm air when it's moving (only when it's moving). If you set it to the lowest say 65 and then press OFF, it will blow cold air (only when moving). Is that how it's built? Pls help.