I’m about to purchase a used WS 4700SF. The heat and AC work great, but when you put the selector on face, it only blows out of the far left vent and the defrost area. A couple of the other settings are off as well. Owner says it needs a new blend door. Would that be accurate?
Oh, while I have you, as you’re turning the wheel it makes a pretty good whining sound as if you can feel the power steering. Hope that makes sense.
Thank you
HVAC system and dash vents (help)
Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Gix1k, Oct 14, 2025 at 11:12 AM.
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Sounds like the owner is on the money about the blend door. On these WS 4700SF trucks, when the air only comes out of one vent and the defrost no matter what setting you pick, it’s almost always a stuck or broken blend door or actuator. It’s a pretty common issue and fixable, but it’s a bit of work to get to it.
As for the whining when you turn the wheel, that’s usually the power steering pump letting you know it’s feeling some wear. First thing I’d do is check the fluid and make sure it’s full and clean. If it is, the pump might just be starting to go. Not urgent, but it’s something to keep an eye on because it can get worse over time.
If everything else on the truck is solid and the price is right, neither of these are dealbreakers. Just budget a little for the HVAC fix and keep an ear on the steering.tscottme, Gix1k and Rideandrepair Thank this.
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