When it doesn't work it is all speeds not just one.
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2006 GMC Sierra 1500
Question: The heater AC fan works sometimes, when it doesn't work it is all speeds.
Answer #1Autohaus Lake Norman from Autohaus Lake Norman, August 17, 2012, 15:29Journeyman
Most likely you have an issue with the blower control unit. If you have auto climate control, its common for the transistor to fail, even if intermittently. If its a manual A/C system, you may have a bad resistor pack and some years of your truck had a special policy in which GM was replacing them for free.
alot of problems with resisters see if its a warranty or cust assistance issues