Air Speed

WARNING: This page is about a different car, the 2007 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.

The blower motor forces air to circulate within the vehicles interior. The vehicle operator determines the blower motors speed by placing the blower knob dial in a desired speed position or by selecting automatic operation. In manual operation, the blower has six speed selections. The HVAC control module may alter the blower motor speed due to compensating factors. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. In manual and automatic operation, the blower speed temporarily reduces speed during transition between outlet modes.

As the requested blower speed increases, the following conditions occur:

The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur:

The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

Afterblow

Afterblow is a feature that dries the evaporator core by operating the blower motor after the engine is turned OFF. This reduces the amount of microbial growth that can create undesirable odors. The vehicle does not come equipped with the afterblow feature turned ON. If the afterblow feature is required due to an odor concern, it must be turned ON by reprogramming the HVAC control module. Refer to Service Programming System (SPS) .

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate:

The engine has been turned OFF for at least 30 minutes.
The ambient air temperature is at least 22°C (70°F).
The A/C compressor operated for more than 2 minutes before shut down.
The system voltage is at least 12 volts.

Once the above conditions have been met, the following sequence of events will occur:

The blower motor will RUN for 20 seconds.
The blower motor will be OFF for 10 minutes.
The blower will repeat step 1 and 2 above for 2 more cycles.