Help with blower vent randomly changing location
 

Hi all,
I'm working on a 2005 Mustang GT and am having an issue with the vent selector. The knob to change where the air is blowing out of works (ie. floor, dash, defrost, and combos) but sometimes while I'm driving it'll just randomly change.
This usually seems like the dash vents will switch to the defrost, and then back.

It seems completely random, like I could be driving for 10 to 20 minutes and suddenly feel air blowing out of the dash and can hear the pitch of the air flow change.

Also, when it's not blowing out of where it's supposed to, it sounds muffled, like the vents aren't allowing all of the air from the blower through.


What might cause this? I'm hoping this is an issue with the actual switch, and not some dying part buried deep within the dash.
Can anyone give any insight? Thanks.

Never had this happen to me but my guess would be the switch. The actual switch it self doesn't move by it self right. If so you might have a ghost or a squirrel lol. You can probably pick a switch up cheap somewhere and test it out and see if that was the problem. Hope it is and it's not in the dash like you mentioned.

TL;DR: Ain't gonna be just a switch. You might have work to do, of contract a proper mechanic if you're not interested/inclined, or you can just shotgun parts at it and good luck. Read on if you dare. :)

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Just a point of order, it's not gonna be just a switch, as the S197's controls you see are integral parts of the actual climate control module (aka HVAC box). All the HVAC stuff happens right there in the dash in that box the switch gear is part of. That module then tells the SJB to do a couple things like the PCM to turn on the A/C compressor so it knows it's running, but mostly it's its own little world goin' on in there. Therefore the mode switch can't be replaced (easily. I mean, sure it could, but...) The entire module has to be swapped out. Also, they have printed right on that module "SCRAP IF DROPPED", and going over the wiring diagram also shows this to be the entire ball of wax HVAC in the car as well:
https://iihs.net/fsm/?d=40&f=Manual%...System.pdf&p=1
(Page 2 for the Compressor part)

Fortunately, they're pretty cheap on eekBaby. If that's the problem, that's the solution, and it can't hurt to try... except prying the dash apart and all that fun stuff. :p

But I want to double check and be sure. Here's why. There are four door actuators involved with the HVAC in these cars. The air inlet door actuator (fresh vs cabin):
https://iihs.net/fsm/?d=336&f=Mode%2...let%20Door.pdf

The defrost door:
https://iihs.net/fsm/?d=336&f=Mode%2...ost%20Door.pdf

The panel/floor door:
https://iihs.net/fsm/?d=336&f=Mode%2...oor%20Door.pdf

And the temperature blend door:
https://iihs.net/fsm/?d=336&f=Temper...20Actuator.pdf

The defrost door and panel/floor door are separate items. And while I'm sure you're being accurate, I'm asking the dumb questions. Are you positive the panel/floor AND the defroster are both acting uncommanded? Or is it just the panel/floor and the defroster's not part of it? Or is the defroster always on regardless of panel/floor? Or are they all moving randomly?

So... yeah, A, B, C or.. um, A again? :)

A - Climate control is bad/faulty/needs resetting, most likely.
B - Actuator for panel/floor is bad, most likely.
C - Actuator for panel/floor is bad as well as the defroster actuator broken period.

These are of course *guesses* and you need to do proper diagnostics before buying any parts. I mean, if there's a wiring issue (like a rodent got in your car) then that trumps all these modules/switches/actuators by far. You can follow the diagnostics in the manual:
https://iihs.net/fsm/?d=332&f=Climat...System.pdf&p=1

Which will maybe need a scan tool and various other things(tm) to do them. You can also trace wiring, which is tedious and time consuming but will be indicated by the diagnostics anyway at some point if you get far enough.

There is also this I found:
https://www.s197forum.com/threads/ho...ustang.138833/

Which on down has a nice picture of the SJB and instructions on how to pull the two fuses to reset the HVAC box and actuators. When you plug the fuses back in, the actuators will cycle through their open/closed and that will allow the HVAC box to know where the start, middles, and end travels of the actuators, which is necessary for it to know if things are open/closed/juuuust the right temperature... So you might try that and see what happens, can't hurt.

Probably more than you or anyone wanted, but definitely not just a switch. They haven't done 'just a switch' in a loooong time. Packaging and integration, it's the FUTURE... or something... but man does it kinda (siphon with a large amount of negative pressure) if you just wanted to test the switch, eh? :yup:

Hope it helps anyway. Good luck! :nice:

Thank you for taking the time to write all of that up! I appreciate it.

So, yesterday, I did some testing to be sure I wasn't working from fuzzy memory.

https://i.ebayimg.com/images/g/ygEAA...Lk/s-l1600.jpg

The knob has 7 positions and I went through all of them. From left to right

Max A/C - 100% dash vents
Dash Vent - 100% dash vents
Dash Vent / Floor - 50% dash / 50% floor
Off - (shuts off)
Floor - About 50% floor, 50% defroster
Floor / Defroster - About 20% floor / 80% defroster
Defroster - 100% defroster

So, whenever the floor is selected on the right side of the knob, most of it comes out of the defroster, even when the defroster isn't selected.
When it's on the left side of the knob (dash and floor) it worked correctly during my tests.

However, the dash/floor selection is the one that I believe shifts around while driving. I can have it on 4 and it'll sound like it's muffled. Like even though it's blowing 100%, only 20% comes out of the floor and 20% comes out of the dash, so the blower can't move all of the air. Then, at random, suddenly I'll have full air coming out of the dash vents, like it all just woke up and started working correctly.


Going from what you were saying, I'm not sure what direction that leads me. I'll try the test with the fuses,

I doubt it's a wiring issue. The car is in immaculate shape in and out.
The only issues I've had are with these controls. The reason I thought it was the switch is because the first thing I noticed is that sometimes when I have it on dash/floor it won't work at all, and I'll have to wiggle the knob, and it'll start working. But, that just seems more like a loose connection. Not something that'd trigger odd behavior like this. If certain positions just weren't working, I'd figure it was mechanical. But with it randomly changing while I'm driving makes me think electrical.

Hopefully it's the controls. I'd much rather replace the module behind the dash, then get to those actuators way back inside. Plus, as you said, they're not too expensive:

https://www.ebay.com/itm/30422174148...EAAOSwIPFhgbLk

Those actuators aren't that bad to get to overall. You could be working on a Mark VII or Mark VIII where the entire HVAC has to come off the firewall to get to the blend door... Ask me how I know... :p Oh, and worse, when they fail, they fail in *full hot* mode. In the Texas summer..? Yeah. Fantastic stuff right there. :p Even with the fan off, the heat would seep in. That was a bad design by Ford. These four door actuators are really quite lovely in comparison. :)

But yes, it sounds like it's the switch, and sounds like a new module is in order. However, if I might offer one more idea, take it as you will... maybe just take apart the module, carefully of course, and spritz the switch with some contact cleaner and flip it around a bit. Might be all ya need. I want to say you can unclip the backing off the module, and the knobs should just pull out... :dunno: Haven't done it myself, but it might be worth tryin' if you feel like it.

Good luck, let us know the results of your travails! :yup: :nice:

Did you ever figure this out
 

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I have been dealing with this exact issue. I replaced the control and actuators. Still doing it. I have a 2009 v6 mustang

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KC

Welcome back, OneCoolGT :nice: