Circuit/System Description

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

The auxiliary blower motor is able to be controlled either by the front auxiliary HVAC control assembly or the rear auxiliary HVAC control assembly. This is accomplished through the auxiliary HVAC control assembly. With the front HVAC control assembly blower switch is in the LOW, MED, or HIGH positions, the front auxiliary HVAC control assembly retains full control of the auxiliary HVAC blower motor by directly applying a ground to the blower motor switch. When the front HVAC control assembly blower switch is in the LOW, MED, or HIGH position, the rear HVAC control assembly inputs are ignored by the auxiliary HVAC control assembly.

When the front auxiliary HVAC control assembly blower switch is placed in the AUX position, control of the system is given to the rear HVAC control assembly. When the front auxiliary HVAC control assembly blower switch is placed in the AUX position, the signal circuit between the front auxiliary HVAC control assembly and the auxiliary HVAC control assembly is grounded, indicating that control should be given to the rear auxiliary HVAC control assembly.

The front auxiliary HVAC control assembly or auxiliary HVAC control assembly applies a ground to the appropriate auxiliary blower motor relay that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:

Low speed, 2 resistors
Medium speed, 1 resistor

When high fan speed has been selected, the blower motor switch applies a ground to the coil side of auxiliary high speed blower motor relay which energizes the relay and provides B+ voltage to the auxiliary blower motor.