HVAC whistle while on recirc

[firefighter_2000]

Over about 60 mph with the A/C on recirc, I have a whistle coming from the system. I can turn off recirc and it goes away. I've checked the filter & filter door, and they're in proper position. Could it possibly not be closing off completely? Any ideas on a fix?
Craig

 

[petersonj]

It is possible the noise is coming from a faulty seal from one of the entry doors or one of the side windows. When the ventilation system is set to outside air (normal), a positive air pressure is generated inside the cabin. Any leaking seal will flow air out of the cab.

When the ventilation system is switched to re-circulation mode, a negative air pressure condition is generated which can cause turbulence with outside air flow right next to a faulty seal. If there is a leaky window or door seal, this turbulence can sometimes be heard in the re-circulation mode.

Listen carefully to verify exactly where the sound is coming from.

- John

 

[firefighter_2000]

It is possible the noise is coming from a faulty seal from one of the entry doors or one of the side windows. When the ventilation system is set to outside air (normal), a positive air pressure is generated inside the cabin. Any leaking seal will flow air out of the cab.

When the ventilation system is switched to re-circulation mode, a negative air pressure condition is generated which can cause turbulence with outside air flow right next to a faulty seal. If there is a leaky window or door seal, this turbulence can sometimes be heard in the re-circulation mode.

Listen carefully to verify exactly where the sound is coming from.

- John

Never thought of that. I’ll check in the morning.

 

[Diesel85]

Do you have those pop-in track style window vent shades?

 

[firefighter_2000]

Do you have those pop-in track style window vent shades?

I do. I’ve had them since I’ve had the truck, and this only started recently.

 

[Diesel85]

I do. I’ve had them since I’ve had the truck, and this only started recently.

I'd go around and make sure they are in the track correctly. Takes all but a few minutes and it's free.

 

[firefighter_2000]

I'd go around and make sure they are in the track correctly. Takes all but a few minutes and it's free.

All in good & solid

 

[Topzide]

@firefighter_2000, By chance do you have a rear window slider? Check the drain and all window seals there also. Make sure the drain is clear for the HVAC box and no debris seen under the cowl vents. Any air flow disruption can create a whistle in these trucks. Good luck narrowing it down.

 

[BigPapa]

Just crack a window and see if it quits.

 

[petersonj]

Just crack a window and see if it quits.

He may not have a rock nearby.

- John