Vents stuck on defrost

chapters707

Member
Jul 13, 2014
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Hi, i drive a 96 mustang and the vents are always stuck on defrost. I know the common cause of this would be a broken vac line as I had that issue on my old 94 and that fixed it. I've inspected all the vac lines under the hood and they seem to be in good shape.

I also verified that I am getting vacuum pull behind the dash at that little black vacuum canister above the blower motor. As far as I could tell all the colored vac lines behind the dash seem to be in good shape and connected as well, and i've tried replacing the ac control switches with one from the junkyard with no luck.

At this point what I've read online is that the only likely culprit is the vacuum canister under the dash might be leaking? Does anyone know if that's the little black canister directly above the blower motor on the passenger side? Or is it that larger canister behind the instrument panel on the drivers side? If its the latter then I dont even know how to get it replaced without pulling the whole dash. I did find the smaller black one on ebay for pretty cheap and its extremely easy to replace, so I'll try that if its a possible source of this problem.

My last idea was maybe a bad blend door actuator? But I don't even know what that looks like and can't seem to find the part online. Maybe thats only for newer cars where the vents work off the electrical system? Idk any insight on that would be appreciated.

If I can't figure out how to fix this the right way i was considering finding a way to jimmy rig the vent doors so it always blows through the main vents. If anyone could direct me to where they're located and what orientation would direct the air that way that would also be appreciated.

I love this car and the ac blows very cold, summer is just coming up and it will be well up into the triple digits in a month or two here, so I'm hoping I can figure something out. Sorry for the wall of text just trying to provide all the details! Hope some mustang gurus out there can send me in the right direction!
 
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I don't have the same year Mustang you do so bare with me...


This is what a typical vacuum operated blend door actuator would look like:

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This one may even be [the] part for your car but the intwerbez being the bastard child that it is, I couldn't say for sure.