I have a 1999 Toyota Corolla 4 cylinder 3 speed auto transmission with around 112,000 miles. This thing gets warm when you use dash or floor or combination. As soon as you turn it to defrost, it kicks the AC on ( I know this is normal in order to remove moisture from the cab) the thing will start blowing cold air out vents. Turn it back to dash or floor and it will take 3 min to become hot again. I replaced the thermostat and flushed the cooling system to ensure it is good. I ran the engine to get it to cycle the engine fan and it cycles fine and coolant apears to be circulating fine. I touched both inlet and outlet to heater core and they are hot to the point you cant hold them very long. Im not sure what to check next. Is there a ambient temp sensor that senses outside air in order to control the AC on heat? Anyone have any ideas? I have pulled the console the dash checked all the linkage and door operation I could find. I did not see any valves inline to be stoping the flow when defrost is used. The coolant lines to the heater core remain hot in this position as well. Any ideas?