98 Ranger 2.5L Auto.

Is it normal to have the air selector switch in the OFF position and yet have air come out of the floor vents at all times when the truck is moving? It's only when the truck is moving acting like the vent is on. I hear a slight air hiss at the switch where all the air lines connect, so i changed that switch and I still hear the air hiss. I can plug the lines with my finger and the air hissing stops so i thought maybe the selector switch went bad allowing air to escape and the vent doors not closing properly or something. So I guess i'm asking if others having air on the floor with everything shut off?

 

Vent diagram seen here: https://www.ranger-forums.com/genera...s-63683/page2/

Door positions are labeled, NV-no vacuum, V-vacuum, and PV-partial vacuum

With no vacuum any air would be directed to Defrost vent, Floor should be cut off as Panel would be, NV position

So floor-panel door is stuck or its vacuum motor is, try selecting panel and floor separately to see if door is moving

The Temp/Blend Door is electric

The fresh air door is vacuum but only used, closed-V, in MAX AC position, normally it is NV

As for the air you hear, system is vacuum operated so any small cracks in a hose would allow air to be sucked in.
Vacuum reservoir in the engine bay holds vacuum for this system.
And it should hold it for quite a while, vacuum isn't used up, just sucks in air and gets lower.

So with engine running turn fan on and set vents to panel, so you can feel the air blowing
Now shut off engine, then turn key back on
Should take a few minutes for vacuum to dissipate, air will start coming out Defrost vent as that happens, i.e. Defrost vent = no vacuum

 

All functions of the vents work as they should. The floor door vent shuts 100% when directed to any other vents but when directed to OFF all other vents will shut and door vent opens allowing air to flow from the outside.

 

Outside air should be directed to Defrost vent, since it would be the only path if floor/panel door was closed(NV)

So in OFF position the floor/panel door is opening a bit, when it should be closed

 

I have discovered the cause. I guess Rangers are notorious for the vacuum line under the hood going to the heater control valve breaking off due to heat from the exhaust over years. So that being such a vacuum leak i'm guessing it wasn't moving the door behind the glove box that determines inside/outside air.

 

??

None of the vents would respond if that line was broken, you would be stuck on Defrost

There is a Black line and a Grey line coming out of the firewall from the cab
Black line is the Vacuum from reservoir, vacuum source for cab selector
Grey line goes the heater hose control valve

 

Yes it was the grey line going to the heater control valve. It was completely broke off where the L fitting was that slides on the valve. I just took out the broken part out of the L fitting and re-inserted the line. Yes all my vents, defrost, floor, facing vents worked still individually with it just hanging there in the engine compartment.

 

I had the same problem. Just pull the remnants of the old line out of the u-bend connecting the old line to the heater control valve using needle nose pliers (it might require a bit of force if its never been removed before. Mine came out after a bit of tugging and twisting) and push the unbroken part of the line back into the u-bend until you can't move it any further. The inside of the u-bend on my 1999 V6 3.0L Ranger has a lip that seals the connection between the line and heater control valve so no adhesive required!