My heater wont work it blows but not hot air. even when warmed up.

What is your question?

the a/c works fine and and defrost its just when i turn it to hot it wont put hot air through its only cold. and my thermostat gauge is showing the car is heating properly and staying at the right temperature. hasnt went down or up in temperature while driving.

What makes this problem better or worse?

doesnt matter if the engine is hot or cold

How long has your 2002 Ford Mustang had this problem?

it stoped about the third time using it in winter