A/C blower motor

99 buick. The blower motor stops blowing, if I tap on the plastic cover on the fire wall, or hit a bump, it will blow fine, but then slows down after a few minutes. Tap on the cover again and it starts blowing again.
I checked the wiring going into the plastic cover and it it fine.
I don't know what is under the cover, if it is the motor or what, but tap on the cover and it starts working.
Anyone ever have this problem?

I have had this problem with my Bonneville, and it was a burnt connector . You should disconnect the harness and check. You can get this connector from your local dealer.

Check the connections and ground to the blower motor. If they are okay, replace the blower motor.