2002 Chevy Silverado BLOWER SWITCH

I had the same problem at about the same milage. The problem probably isn't the fan motor or the switch on the dash. It is probably the resistor block that controls the fan speed. It is located under the dash on passenger side. You may have to remove the black cover next to the floor and firewall. Follow the wires down from the dash switch to the air plenum behind that cover. The resistor block is inside the air plenum (2 screws to remove). The circuit printed on the board may have one or more shorted out areas (may be burned looking. This block is what acrually controls fan speed. You could try to repair the shorted areas with solder. A new one will probably be around $50.00 at the dealer, they can be found online for around $30.00. Hope this helps

Hope this helps

http://www.2carpros.com/first_things/blower_motor_high_speed_only.htm