2008 Explorer hvac won’t go to floor setting

[relentless85]

2008 Ford Explorer 4.0L. When I turn the hvac knob to change it to where the air is supposed to come out the floor, the air comes out of the defrost position in the dash.

I know that is the “default” location the air comes out if the hvac system looses vacuum.

So I don’t know where to start looking for the vacuum leak or what parts to replace. I know a few years ago I replaced a check valve in the engine compartment that had to do with the hvac system but it did not fix it.

When I am driving, I hear a hiss sound coming from the black resivour that is under the passenger side dash area. The hiss is more pronounced when I am giving the engine gas and increasing in rpm. The resivour does not appear to the cracked.

The control knobs on the dash have a little crack near the air location selector knob, could I be loosing vacuum there?

Is there a diagram somewhere I could look at to see where the vacuum lines run and what the part numbers are for the lines, check valves, resivour and control knob module?

 

[relentless85]

2008 Ford Explorer 4.0L. When I turn the hvac knob to change it to where the air is supposed to come out the floor, the air comes out of the defrost position in the dash.

I know that is the “default” location the air comes out if the hvac system looses vacuum.

So I don’t know where to start looking for the vacuum leak or what parts to replace. I know a few years ago I replaced a check valve in the engine compartment that had to do with the hvac system but it did not fix it.

When I am driving, I hear a hiss sound coming from the black resivour that is under the passenger side dash area. The hiss is more pronounced when I am giving the engine gas and increasing in rpm. The resivour does not appear to the cracked.

The control knobs on the dash have a little crack near the air location selector knob, could I be loosing vacuum there?

Is there a diagram somewhere I could look at to see where the vacuum lines run and what the part numbers are for the lines, check valves, resivour and control knob module?

Also I noticed yesterday that sometimes when I’m giving the engine more gas than usual, say to merge onto the highway, the air will go to defrost location for a few seconds then return to the dash vents.