Noise near blower motor behind dash?

[Ethereal_Zer0]

What's behind the glove box area that is HVAC related and has some kind of valve/flap that eventually opens? It sounds like it opens when the car gets up to temp when I am using the defroster. Sorry for the crappy description, it just makes a weird noise when it opens and I suspect whatever it is may be getting stuck occasionally. Trying to be prepared in case something craps out on me lol.

I'm assuming there is some kind of vacuum or temperature controlled something or other back there? I don't think it is the blower motor, though maybe something attached/connected to that? The noise I hear comes from that general vicinity.

Many thanks and Happy New Year!

 

[gkomo]

I’ve had to take that assembly out to reseal and clean it up. There is a door/flap in it that open closes. Removing and replacing the hvac box/assembly isn’t “easy” but definitely not hard to do.

I documented my experience in my progress thread “Komos 1990 GT” somewhere in there.

 

[AeroCoupe]

Was this it?

Progress Thread Post in thread 'Komo's 1990 GT - Parts Gathering Purgatory'

Mar 24, 2025

Got the blower motor all cleaned up and back together with new seals:

Old:





Mid cleaning (getting the adhesive off this flap was a pain):



New:





One thing I did not like about the LMR kit was the butyl strips were completely stuck to the package they come in… basically had to just rip chunks off then ‘roll’ them into the right shape and place them in the channel.

• gkomo

• 

 

[gkomo]

Was this it?

Progress Thread Post in thread 'Komo's 1990 GT - Parts Gathering Purgatory'

Mar 24, 2025

Got the blower motor all cleaned up and back together with new seals:

Old:





Mid cleaning (getting the adhesive off this flap was a pain):



New:





One thing I did not like about the LMR kit was the butyl strips were completely stuck to the package they come in… basically had to just rip chunks off then ‘roll’ them into the right shape and place them in the channel.

• gkomo

• 

Yes thank you for going back and finding it.

I think this is what he’s talking about

 

[Ethereal_Zer0]

Thanks, that's probably what I am hearing. What's that called and how does it operate? Does it open at a certain temperature? Certain pressure? Just curious since I don't know anything about HVAC stuff. My car had the A/C removed, but I think it still has the heater core and everything else (defrosts and heater will blow some hot air). I've been replacing vacuum caps and lines in my car over the last year, I'll have to crawl down there and replace any lines I find just as a precaution.

 

[Mcmahst]

Not sure if this will help answer tje question, since I don’t know what year your car is:

http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

At least it will give you an idea of what components are likely the issue. Good luck.

 

[Ethereal_Zer0]

Not sure if this will help answer tje question, since I don’t know what year your car is:

http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

At least it will give you an idea of what components are likely the issue. Good luck.

Thanks, that gives me a better idea of what all is back there! I have a feeling it is the defrost door, it seems like that is typically when I hear it open (while defrosting). I'll pay more attention now, but in the past when I have been messing around with it I have changed the settings going from defrost, vent, floor and sometimes it would flap open. Now that I know that is indeed all vacuum controlled too I'll definitely check for leaks.