91 mustang 122k completely stock
When I turn my heater on it blows hot for a second and then stops the heater core isn't leaking both line at the firewall are hot. Could it be a blend door issue let me know thanks
Blend door is strictly mechanical. If you turn the hot/cold selector, you should be able to feel/hear the blend door activating. On the pass side of the car, flip the glovebox down and you'll see a black cable which is the blend door cable. You can see where it attaches on the HVAC box. If you move the selector, you should see it move the level for the blend door up and down.
It's also possible you have a blockage of the heater core which is not allowing coolant to pass. Most heater hose setups have a restrictor with a reduced diameter. One good chunk of rust or crud from the radiator would be all it takes to clog it up