Cabin air flow

[mikkelstuff]

I now realize that the A/C is working fine in my 2002 Ranger XLT but I'm just not getting air flow out the dash vents for a few minutes. Instead, there is air flow out the defroster vents. From what I read, this is the default condition for a poor system vacuum.

I removed the vacuum reservoir and checked it with my Mytivac only to find that it holds a vacuum just fine and the check valve is working correctly.

I then put the Mytivac on the vacuum line into the cab (ignition off) but the in-cab system will not hold a vacuum. Should this be expected or does this mean a vacuum leak in the interior air flow control system? If so, any place to start looking?

 

[rubydist]

It should hold vacuum. Most commonly, the plastic vacuum line is cracked or broken somewhere. But it is also possible that one of the diaphragms in the vacuum motor on one of the actuators has a leak.

 

[RonD]

Vacuum diagram seen here: https://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

If you look up under the glove box near right edge of firewall you will see a white and black vacuum line coming in from engine bay
The Black line is the vacuum from reservoir
The white line is vacuum out to Heater hose by-pass valve, changes to Grey line in engine bay
This white hose is also used to close fresh air vent in MAX AC setting

Picture of inertia switch here, just above it you see the black and white vacuum lines going thru firewall: https://www.explorerforum.com/forums/attachments/fpi-jpg.198133/

If you fold down glove box door all the way you should see a vacuum hose manifold on the left side, several colored hoses connected together
This comes from the Climate Control panel and then out to the 3 "vacuum motors" in the cab

You can hook up your vacuum gauge and then try the different settings on climate control panel to see if only one or two settings cause loss of vacuum
To narrow down where the leak is

As said the most common leak is the black hard plastic vacuum line that runs in the engine bay to the fire wall, it can melt near exhaust or crack

Climate control Reservoir is same as power brake reservoir, should hold vacuum indefinitely
When you first get in a vehicle and press down on the brake pedal you can feel if it still has vacuum in the booster or if it has been lost over night

 

[mikkelstuff]

I was able to find a "vacuum harness" on ebay which has the two hard vacuum lines - engine to reservoir and reservoir to firewall.

I see this comes with an, ah, bulkhead fitting which inserts through the firewall. Any advice on changing out that bulkhead fitting? Unfortunately this is buried under the A/C so I assume this has to be changed out from under the truck.