Front and rear blower relay
WARNING: This page is about a different car, the 2003 Dodge Grand Caravan, 2003 Dodge Caravan, 2003 Chrysler Voyager, and 2003 Chrysler Town & Country. However, it is still accessible from the selected car via links, so may be relevant.
The blower control switch is part of the Automatic Temperature Control (ATC) or A/C-Heater Control Module, (Manual Temp). When the blower switch is turned on, the ATC or A/C-Heater Control Module sends a PCI Bus message to the FCM. The front and rear blower relay is then powered through low side control on pin 30 of the FCM. The relay provides the high side to the blower motor, and the blower speed is governed through low side control in the ATC or A/C-Heater Control Module. This circuit is electronically controlled and continuously monitored for malfunctions.