2003 Impala blower fan not working

So when you start the engine, the blower stops working?

That sounds like an ignition switch.

Roy

Yep, sounds like an ignition switch

Roy

Procedure below

Roy

1. Disconnect the battery ground cable. See: Negative > Service and Repair

2. Remove the steering column opening filler panel. See: Steering Column > Removal and Replacement > Steering Column Filler

3. Remove the knee bolster bracket.

4. Remove the instrument panel (I/P) cluster trim plate.
Impala See: Dashboard / Instrument Panel > Removal and Replacement > Instrument Panel Cluster (IPC) - Trim Plate Bezel Replacement
Monte Carlo See: Dashboard / Instrument Panel > Removal and Replacement > Instrument Panel Cluster (IPC) - Trim Plate Bezel Replacement

5. Remove the ignition switch bolts.

6. Lower the ignition switch away from the instrument carrier.

7. Insert the key into the ignition lock cylinder. Turn the key to the ON/RUN position.
8. Depress the retainer to release the transaxle park/lock cable. Remove the park/lock cable from the ignition switch by pulling on the cable.

Important: You cannot remove the Passlock electrical connector until the lock cylinder is removed.

9. Depress and hold the detent on the bottom of the ignition switch in order to release the ignition lock cylinder. Remove the ignition lock cylinder with the key.

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10. Disconnect the Passlock electrical connector.

11. Disconnect the electrical connectors.

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12. Use the following procedure if the ignition switch lock cylinder is seized or won't rotate:
1. Protect the immediate work area with suitable material such as clean shop towels or a clean fender cover.
2. Locate the surface for the release button (2) for the ignition switch lock cylinder on the plastic ignition switch housing. Center punch a location (1) on the rib approximately 3/8 inch reward, toward the key entry end, from the cylinder release button.
3. Carefully drill a pilot hole through the plastic housing with a 1/8-inch drill bit.
4. Using a 9/32-inch drill bit, carefully drill a larger hole at the pilot location, and slightly into the surface of the ignition switch lock cylinder, to break the release button retaining spring.
5. Remove portions of the broken spring from the hole using a small suitable tool.
6. Grasp the ignition switch lock cylinder and remove the cylinder from the switch housing.
7. Remove any plastic flash from the drilling operation, and using compressed air blow out the ignition switch assembly.
8. Follow Service Data procedures when cylinder coding is required. See: Ignition Switch Lock Cylinder > Removal and Replacement > Key and Lock Cylinder Coding