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GMC Forum: 04 Yukon Denali A/C on during "defog"
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Old 10-16-2017, 10:03 AM
mdbelanger mdbelanger is offline
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Drives a GMC Truck
Join Date: Oct 2017
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Default 04 Yukon Denali A/C on during "defog"

So I was getting crap for gas mileage less than before. In troubleshooting I noticed that the A/C compressor is engaged when the climate control is in "defog" mode. That's the symbol that show air on front window and floor. Its off on all other air vent settings. My question is that normal or typical? None of my other vehicles have done this when the A/C is off. It is not in auto, the a/c is off but the compressor is engaged when in this mode.
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Old 10-19-2017, 07:04 AM
Daddio Daddio is offline
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Drives a 2014 GMC Yukon, 2005 Lincoln LS, Massey Ferguson 165, 1956 Thunderbird, 1959 Cadillac Biarritz
Join Date: May 2017
Location: Prince Edward County, So Ont
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I think that's normal, at least it was for my 02 and 14 Yukons.
The theory is; the air conditioned air is drier and, when blown across the windshield, more quickly dissipate the fog. Heated air is mixed in as well, and the blower usually kicks in to a higher speed. The A/C snow flake isn't illuminated on defog either.
I used to get after my wife to not leave the control on defog all the time so gas mileage isn't as bad.
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Old 10-19-2017, 08:59 PM
mogleybear mogleybear is offline
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Drives a 2012 GMC Sierra 1500 Crew Cab
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Location: Jemez Mountains
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Yes, normal. The A/C runs in defrost / defog mode.
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Old 02-12-2018, 12:18 AM
Paul Sebesta Paul Sebesta is offline
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100% normal!
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