CTS 2003-2005

Description & Operation


The blower motor is a variable speed motor. The higher the voltage applied to the motor, the faster the speed. Depending on the HVAC (Heater Ventilation Air Conditioning) option installed in the vehicle, blower speed control could be through a set of resistors or through a solid-state blower motor control module.

Battery voltage to the blower motor is supplied by the heater & A/C control by way of the blower resistor (or blower motor control module). At low and medium speeds, the voltage is stepped down by the blower motor resistors. At high speed, the blower motor relay is energized, removing the blower motor resistors from the circuit. Battery voltage is then applied directly to the blower motor through the relay. The motor will then run at maximum speed.

Several types of HVAC systems were available on these vehicles, from manual to fully automatic electronic control. The blower motor speed can be adjusted manually by pushing the fan switch up or down or automatically by placing the heater & A/C control in the AUTO mode.

In general, this system is reliable. Because so many of the control operations are electronic, special diagnostic equipment really should be used for system diagnostics and check-out. An authorized technician using a scan tool can most quickly locate HVAC problems.

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Fig. Typical behind-the-instrument panel view of HVAC related components. Depending on the HVAC option, not all components are used on all vehicles

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Fig. Typical HVAC operation schematic

An inoperative blower motor could be caused by the following:

Blown fuse(s). The fuse should be replaced. There may be both a LOW BLOWER and HIGH BLOWER fuse. Some models may also call it the HVAC fuse. Even the RADIO fuse is used in some applications. Check them all. If a fuse is blown there may be a short to ground in one of the power supply circuits.
Open Circuit. Check the circuit between the ignition switch and the blower motor, and the blower motor ground circuit. Repair as necessary.
Faulty blower switch. A faulty blower switch should be replaced.
Most heater blower circuits also include a blower motor relay (look in the underdash convenience center), as well as a blow motor resistor. These items should be checked especially if the blower runs in one or two speeds, but not all speeds selected.