Fresh air vent?

[nikojo]

My M998 truck has OEM AC system from more recent truck installed which includes heat.

The heat blows well including on the defrost setting on the windscreen through the new plenum.

But when the truck is traveling at speed I can feel very cold air getting through the original vents right next to the windscreen.

How is this possible? Where is that cold air coming from?

Is there some outside air intake tied into the original defrost vents???

 

[nikojo]

Bump

 

[SmartDrug]

Is the fresh air intake on the right hand side of the tub open or closed?

 

[nikojo]

Closed. Assuming thats the round screen that turns to close.

But that isn't connected to the vents/plenum along the windshield that's built into the dash.

 

[SmartDrug]

Mine is, but I have an A2 truck.

 

[nikojo]

I have the new plenum from the A2 trucks but also the older built in plenus with the cutouts along the windshield.

Don't understand what that's attached to and how the air is getting into it.

 

[SmartDrug]

There are flexible pipes that attach to the rigid plastic vents in mine, if those became detached, it could allow for air to flow into the cabin in my setup. You can see how they attach by removing the doghouse and then removing the upper cover that runs longitudinally across the dash just on the back side of the firewall.

 

[nikojo]

Got it. I do remember that vaguely from the manuals.

But what I still don't understand is if those are all disconnected how does the outside air get in there??

Are there gaps in the firewall that would allow for that?

Can that panel be removed without removing the windshield, ie the louvered vent top?