This winter my heater motor seized up from corrosion. Yours may be failing due to corrosion or brushes or it may have failed due to faulty electrics, but check the easy stuff first like I did. Chances are the motor will have to come out for a little TLC
-Torx bits
-Nut Driver
-Headlamp (A wonderful tool for any repair)
-motor or gearbox oil

1. Spin the motor by hand, grabbing the fins through the cabin filter housing.
-Feel for resistance, this indicates corrosion. Not resistance could indicate electrical problems.
-You cannot lube the shaft thoroughly from this vantage.
2. Removed the motor from under the dash.
-Nothing technical just a pain in the ass. You'll have to remove a few body panels and bend an HVAC tube. You wont break the HVAC tubing but you may break some of the flimsy white plastic.
3. With the motor out you'll want to lube the bottom shaft with a heavy weight oil, and then check the brushes.
-My brushes were more than 50% gone and you may want to replace your's. It was -10F outside so this wasn't an option. I had the brushes eventually go out in my 9-5.
4. Reinstall and enjoy heated air that moves!!
-You don't need to tape the screws to the blower housing just because its upside down.

Not sure what the rules are on posting links to threads over on Saabcentral but this thread helped me pull the motor out(ACC Blower R & R: How To - SaabCentral Forums)