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Randall C
Randall C, ASE Master Tech
Category: GM
Satisfied Customers: 12803
Experience:  ASE Master Tech, 35 years, Foreign/Domestic repairs
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2007 chevy truck, when I turn off the ignition, the defrost

Customer Question

2007 chevy truck, when I turn off the ignition, the defrost fan on front window begins to blow and ran down battery
JA: Have you tested the battery with a voltmeter? And can you see if it's leaking or not?
Customer: battery is good
JA: What is the model of your '07 GM?
Customer: LT 6.0 4x4
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: yes. nothing
JA: Anything else you think the mechanic should know?
Customer: 148000 miles
Submitted: 11 months ago.
Category: GM
Expert:  Randall C replied 11 months ago.

Hello, do you have the manual HVAC or full automatic climate control?

Customer: replied 11 months ago.
auto climate control, you can set the degree temp
Customer: replied 11 months ago.
I leave the ac on the auto mode with a temp setting, then when I turn off the truck, the blower changes to blow the defrost vent on windshield and continues to run.
Expert:  Randall C replied 11 months ago.

Thanks, ***** ***** return shortly

Expert:  Randall C replied 11 months ago.

Ok, there is a standing recall for blower running all the time on the "manual system". on the auto? there is not. Likely what has failed is the blower control module. On auto system its a module and NOT a resistor, When these module fail? they will cause symptoms just as you describe. It is not that uncommon on GM vehicles to have this happen. I have attached a couple links showing location etc, up under passenger side of dash. I have to lean to this as most common we see, very rare instances the control panel is at fault but that is rare

Customer: replied 11 months ago.
ok, but where is the module? I cant tell from the diagram, what number would it be.
Expert:  Randall C replied 11 months ago.

its #8 and the second pic ture I sent shows it being removed, Its up under passenger side dash, You remove the sound panel under dash , you will see the blower motor, the module sits along side of the blower and has a plug to it, Held in by 2 screws. hers the picture again