Need some help on high pitch whistling noise when fan is on

[UATahoe]

Ok. So i just recently finished putting new weatherstripping everywhere in my 87 pickup. Now when i turn on the fan i get a realy high pitch whistling noise. Here is the strange part though. If i put it on max AC, it is as quiet as can be on every fan speed and not a single problem. Hear nothing. But on any of the other remaining settings (reg ac, vent, heat, defrost) there is a really loud whistling noise on all fan settings except the lowest setting. And you can almost feel the pressure effecting your head. I am stumped on this one. Any help????

[Eyegore]

Believe it has something to do with pressurizing the cab, when on the ac settings it cycles through the system and not through the cab. When on the vent and heat it must move the dampers to become paritially open and causing the whistling.

[UATahoe]

Well, on the max ac i hear nothing. On the reg ac i hear the same noise as on the heat vent and defrost settings.

[James McClure]

UA. "Max" is the old "recirc" setting. This recirculates air in the cab volume for volume so no pressure\vacuum will exist. At ANY of the other settings, fresh air is drawn into the cab. This creates a high pessure area inside the cab as related to outside ambient atmospheric pressure, hence the whistle. Finding it isn't going to be easy, but using a stethescope with just an open end should help. Run the truck and put the controls to duplicate the noise. Using thee open end of the scope, trace EVERY gasketed area until you track it down. When I redid my truck the new gaskets made it almost impossible to shut the doors without opening a window. I had wind noises also. Found mine to be in the vent windows, they wouldn't close all the way, gaskets would turn in just a bit. A little silicone spray fixed that. jim

[UATahoe]

Jim, thanks! The vent window seals were reokaced on mine also and they sound awful even though they are new. I will try to track it down and see whats up. Sounds like it will be fun. LOL I am tempted to seal off the vent windows from the outside and just keep them shut. The wind noise from them is just awful.

[Keith Seymore]

Yep - you are pressurizing the cab. Rolling the window down just a skotch will make it go away.

You don't hear it on MAX because it is recirculating the air rather than drawing from the outside.

And - the windnoise from the vent window is, in fact, awful. Even when new.

K

[UATahoe]

LOL no doubt. I am just giving up on them. Would a bead of clear silicon around the outside edges seal it off well enough to get rid of the noise?

So far, my solution has been to barely crack the back slider. I may just stick with that for now.

[Keith Seymore]

Originally Posted by UATahoe

LOL no doubt. I am just giving up on them. Would a bead of clear silicon around the outside edges seal it off well enough to get rid of the noise?

So far, my solution has been to barely crack the back slider. I may just stick with that for now.

One of the things you could try is taking the Pressure Relief Valve out of the bottom of the door; that might provide enough airflow to make the whistle go away. (Then you run the risk of cold air flowing back in, depending on the climate where you live).

But I just touch the side window, rolling it down just enough to make the whistle stop.

K

[UATahoe]

Awesome. Thanks Keith! What does the valve look like? I am not familiar with it. I live in Alabama so cold air wouldnt be a problem. Hot maybe but i might try it out to see.

[Keith Seymore]

It mounts behind the louvers in the door, one screw on each end.

It's a small plastic frame with little rubber flaps that hang down.

It may not make much of a difference in terms of air flow (outbound) but could put you over the edge.

K