I'm having vacuum issues with my 2000 Excursion. Under part throttle the A/C blows out the defroster ducts. Also took it up a trail and engaged the 4WD for the first time, and the hubs didn't lock. I've verified everything under the hood is in good working order, all the lines and connections are good, the reserve tank is good. What I can see under the dash appears to be in good shape as well.Can anyone point me in the direction of a good resource for a vacuum diagrams?

 

Autozone's website might have a diagram, but I have a simple test. Get a can of starting fluid or WD40 (hair spray will probably work to some degree) and with the engine running spray around the hoses. If the motor rev's up, then you sprayed near the leak.

 

Have you checked the connections at the hub itself? That is a known place where they either pop off or crack and come off.

 

Are you sure the leak isn't from a hub? Did you clean and grease them ?That should be the first step.

 

What puzzles me most is that the A/C switches from the vents to the windshield dependant on throttle. It seems to have normal vacuum at idle and cruising down the highway. But take off from a stop, or climb even a slight hill, and the A/C loses it's mind.

I have only had the truck for 3 months so far, and I still have a ton of maintenance and upgrades to do. It's in pretty good shape overall though, so I'm trying to work out the big bugs like this first.

 

Grease your outer hubs first. There is a thread in here somewhere that gets pretty deep into the intermittant defroster thing. Do a search.

 

been there ...none that.... my problem was the auto hub themselves. vacuum moves the hub in and out of 4x 4. i replaced the hubs ( one hub was locked up so bad that it would not turn even with the big channel locks ). i went to replace the auto hub ... they were $325 each from Ford ( no aftermarket ), warn manual hubs $ 194.00 a pair from napa. i lost the auto locking 4 x 4 but it fixed the vacuum problem.

 

AND you got a better set of hubs !

 

Before you shell out the cash on the new hubs, check the 4wd switch itself. I didn't quite turn it back to 2wd one time & the same thing happened to my A/C. Vacumm was routing around the switch ( so to speak) and there wasn't enough left to close/open the damper of the A/C.

Just my 2 pennies. Best of luck & let us know what fixes it.


Keith

 

Doesn't the wrecking yard have those?

 

I FIXED IT!

For $1, yes, One Dollar!

So I was looking at a thread on another forum that showed the exhaust manifold from the wheel well. It also showed the vauum line for the hubs nicely. Since the lines appeared to be in the area of the ehasut manifolds, and because I had done an engine repacement just after purchast, I thought maybe I created the problem in that area and either broke or melted a line.

Nope.

The lines are in good shape, away from the exhaust, and not melted or broken. Since the hubs themselves operate normally by hand, I'm having a hard time rationalizing that the hubs are the problem. So I traced the vacuum lines from the wheels to the vacuum tank and the lines are all in good shape. I also checked the lines on the A/C-Heater side of thetank and they are al in good shape too.

Since everything else checked out, there was only one section of line that I could not see going behind the heavy wires to the charging relay on the inner fender and connecting to the hub vacuum switch.

And there it was.

Both the red and black lines were damaged. The red line was completely severed. The black line was worn 80% through and was barely hanging together. I drove 2 minutes to Autozone and bought 3 feet of vacuum hose that slips snugly over the plastic lines. I attached both ends of the line to the hub vacuum switch. Then I cut back the plastic cover on the plastic vacuum lines about 1-1/2". I cut about 3/4" off of the plastic lines to remove the damaged section. Since I didn't have anything else, a little spit on the plastic lines let the hoses slide on about 3/4".

I took the truck down the road a couple miles, drove it exactly how it didn't like to be driven for proper A/C function before, and the A/C blows hard and cold. Seems the vacuum leak mut have also been allowing the heater valve to flow hot coolant through the heater core while the A/C was on, really hurting the A/C performance. It's like a whole different truck now.

I'd feel even better about it if it could have kept up with the 6.4L Powerstroke that drove away from me on the A/C test drive, but that's another thread.....

 

Yes it will default to the AC if not holding air

 

No, it defaults to the defroster if it isn't working. It's a safety failsafe.

 

Correct; defroster. I knew I would make a mistake sooner or later.

 

I thought I made a mistake once. But I was mistaken about it!