I have a 2005 Suburban with dual zone a/c controls. With the a/c on, the fan will blow only about half speed. I can manually turn the fan speed down, but not any higher than half, and pushing the recirculate button does nothing. Also, the fan speed indicator on the display will disappear, as does the output indicator (the little stick figure with the arrows showing where the air will blow). My wife tells me when she turned off the key today, the fan continued to blow. It appears the problem is in the digital/LED control module. Any chance it's as simple as swapping the control module in the dash?

 

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The blower motor resistor and resistor module connecter may need to be replaced. This is just a suggestion, not a diagnosis. I encourage you to have the vehicle inspected by a certified technician for an official diagnosis.

Please keep us posted.

Louis
GM Customer Service