AC - Airflow Question

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Jun 1, 2018 | 10:30 AM

Phobos

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AC - Airflow Question

I have a 2018 SC 6.7 XLT. The AC blows cold air, and enough of it when I have it set just to come out the dash level vents. If, however, I add the lower, or foot vents then the air flow decreases to almost nothing. Very little air at both my feet and the dash vents. I then have to crank the fan up to about 75% on the dial to feel air but at that setting the fan is really loud and above regular conversion level.

Anyone else notice this on the non-dual XLT type AC?

Jun 1, 2018 | 10:40 AM

jakematic

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Joined: May 2018

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From: NC USA

What you describe is exactly how my '16 XLT F-150 was, and how the better half's '18 XLT F-150 works.

My 250 has the dual, and I haven't tried anything other than Auto (due to prior similar experience) but will check it later today.

Jun 1, 2018 | 11:22 AM

BenFranklin

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This is typical operation. The fan speed setting must be increased to accommodate the second set of vents opening in order to create enough static pressure for flow out of the vents to occur at an appreciable velocity and volumetric rate. The noise level is a bit annoying, I agree. Unfortunately, I assume the fan is undersized due to the weight and space constraints since we now have F150's essentially...so in order to achieve the same volume from a smaller fan wheel, the RPM must be increased. This, combined with poor vent design, is where the noise becomes noticeable. Don't even get me started on the fact that I cannot adjust the dash vents to a position where they don't hit my face...I miss my 2011.

I love a lot of things about this truck...but basically everything on it that is taken from the F150 sucks. I hate it.

Jun 1, 2018 | 04:42 PM

Phobos

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Thanks, I guess I'll have to learn to live with the fan noise then.

Jun 1, 2018 | 04:46 PM

MPawelek

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I just turn my hearing aids off!

Jun 1, 2018 | 06:19 PM

69cj

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From: Middle Tn.

It takes twice as much cfm to feed 8 vents as it does 4 vents. That also means that all vents are the same size and have the same number of angles in the feed lines.

Jun 1, 2018 | 09:49 PM

Mud Doc

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From: Texas

68cj,
You probably have it correct--doubling the volume to fill requires quadrupling the cfm. So, to double the vent openings, we have to increase the fan speed to get the same output out the vents.