Blower Speed Controller (BSC)
WARNING: This page is about a different car, the 1996 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
The BSC varies blower motor speed by varying resistance in blower motor ground circuit. The EATC module sends a varying voltage signal to a power transistor in BSC. See Fig 1. Current flows through the blower motor and power transistor to ground. BSC has delay function to gradually increase and decrease blower motor speed. A high-speed blower relay, integral with BSC, provides power for maximum blower speed.