I need help fixing my heater. It makes a thump sound.

[.:oZzy:.]

i have a 2002 xlt explorer and my problem is that my heater when it makes a loud thump sound it starts blowing heat. somtimes it wont even do the thump sound at all. i dont know what the problem is and i really need help bcuz i live in northern indiana and its winter time and its pretty cold soo if anybody knos plz help!!!

 

[BrooklynBay]

Welcome to this forum! I've moved your thread into the A/C & heater section. You might have a problem with a vacuum line or the blend door.

 

[.:oZzy:.]

how would i kno which problem it is??

 

[BrooklynBay]

The vacuum lines have to be checked for cracks. Vacuum moves the servo pistons. The blend door actuator is electric. You could see if it's moving.

 

[.:oZzy:.]

i mean i have to start the heater with cold on 4 then gradually move it to heat itll either make the thump then blow heat or just stay blowin cold air