that's gonne be a loose connector at the blower motor (behind the glove box door)
Open your glove box all the way, disconnect the little return string on the right side, then fold the little tabs that are holding the glove box open and that'll let the glove box door move down and out of your way.
Then look at the blower motor and see where the two wires go into it.
if you wiggle that connection, you'll probably find the source of your problem.
Fixing it depends on whether the connector is bad.. or the contacts in the blower motor are bad.
On mine.. the connector was bad.. and over time it's constant turning off and on eroded the contacts in the blower motor.
Dont worry, changing the blower motor is very very easy... you'll see once you get in there.
Hope this helps