ok yesterday i was fidling under the dash, dont ask. well i had the heat blowing hard on the floor so I took the black cover under dash pass side. and while the heat it blowing and cooling down fast. I can feel alot of cold air comming from fan area by fire wall. What im trying to ask is, Is there a air blend door that gets stuck or and I just looking for something not there? I do need to flush heater core or get a new one.