what's wrong with the heater in my car ?

Did you flush the heater core by removing the hoses and blasting a garden hose through the heater core in both directions? if not do that.

Watch a youtube video for replacing the heater blend door actuator. Before replacing it turn the temperature all the way hot and cold while watching the actuator to see if it's moving in both directions or not moving at all. If it's not moving replace it. Make sure the shaft that fits in the actuator can be turned by hand before installing the new actuator. Advance Auto carries the part.

Yes if both heater hoses are hot when the engine is warmed up, then it could be a problem with the blend door of the heater system which is operated by an electrical actuator and that is controlled by the temperature switch of the heater controls. The Blend Door mixes the airflow from the heater core and the AC evaporator core to get the desired air temperature output from the vents. So if you have a good heater core /hot hoses but still are not getting good heat output from the vents, then it could be an issue with the blend door system. In many cases, the electrical actuator is bad and does not move the door properly but it could also be a problem with the door linkage mechanism being stuck or broken or a bad temperature switch or wiring defect. You would have to inspect the actuator and see if it moves through the full range of motion as you change the temperature setting of the dash control heater temp switch from cold to hot ....check to see if the door moves freely with the actuator disconnected.

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