If there is air blowing out, it is not a vacuum line and isn't relevant to the locking hubs or HVAC.

However, I don't have a clue what this line could be and I don't think their should be any line with air coming out of it. Can you get an picture of this? Where it comes from and where it attaches?

 

do you have an e-mail address? for some reason i cannot attach photos.

 

OK. I looked at the pictures in your album.

Ford Truck Enthusiasts Forums - mblanken881's Album: Air Leak (for others reference).

What you're looking at is one of the a/c lines. It goes into the condensor block, which is pressurized by the HVAC fan. The air coming out is from the air being pushed by that fan.

It's not part of your vacuum, 4WD or HVAC problems. It really isn't a problem, other than being wasted warm/cold air. You could seal it up with some spray foam insulation or caulking, etc.

 

OK thanks. Thought maybe I'd found something there. I've checked everything and cannot find a leak anywhere.

 

OK. So when I got home I pulled the lines off of the hubs and stuck bolts in the ends of them to plug them up. The AC still went to the defrost vents for a short time. This tells me the hubs are good, correct? I don't know where else to look. I've checked all the connections and they all seem OK. What should I do????

 

No. What you did tested absolutely nothing.

The pump makes vacuum. It sucks as much air as possible out of the vacuum reservoir.

A vacuum line goes from there into the HVAC controls. Those controls allow vacuum to various vacuum motors that control air flow in the HVAC system.

Another vacuum line goes from the reservoir to the PVH solenoid. When you switch to 4WD, the PVH solenoid is opened for 30-45 seconds. This applies vacuum to the hubs, causing them to lock.

By removing the vacuum line from the PVH solenoid to the hubs, you essentially opened the hub side of the PVH solenoid to atmosphere. When the PVH solenoid opened, it allowed air in, vacuum in the lines and reservoir dropped suddenly, and there was no vacuum to keep the HVAC motors activated and they switched to their default positions, which is the defrost.

If you want to do a test, put a cap on the PVH solenoid hub side port. Then switch to 4WD. With the cap on the PVH solenoid hub side, no air should be allowed in, regardless of the whether the PVH is opened or closed. When you switch to 4WD, nothing should happen to your HVAC. If it switches to defrost, you know you lost vacuum, and the only possible place that could have happened is inside the PVH solenoid itself.

 

OK the PVH has two lines. One going to it and one going to the hubs. They are connected to the PVH in one single plug. I pulled this plug off and started the truck. The line going to the PVH was sucking air. I plugged that line with my finger and left the one going to the hubs open. I then had my wife switch to four wheel drive and the AC did not go to defrost. So is this saying the PVH is bad or that there is a leak at the PVH or after?

 

It's saying there is a leak in the PVH solenoid or after (the line going to the hub). However, if your mechanic put a vacuum pump on the line going to the hub and it held vacuum, then that pretty much isolates the leak to the PVH solenoid itself.

 

Thanks David!! You've been a great help!!!!

 

One more quick question:

What fuse controls the PVH? Maybe the fuse is just blown and thats why it's not working.

 

It'd be one of the 4WD fuses. You can find a list of fuses in your owners manual. If you don't have one of those, you can get it here.

https://www.flmowner.com/servlet/Con...ionalEventPage

However, it's not that your PVH isn't opening (indicating no power), it's that when it opens it leaks off vacuum. So I don't think a fuse would be the issue.

 

Just in case anybody is curious. It was the PVH. Replaced it and everything works fine.

Thanks again David!!

 

that is exactly, to a T, what my truck is doing. How much was the part?

 

don't know. the dealer paid for it. but i've seen other guys on here say they are $51. you have to buy them from ford.

 

great, thanks alot. I haven't looked at this part but it sounds like I should be able to replace it myself. Is that correct. R and R? Thanks to you and your mechanic for figuring out my problem. I was just driving up and down the street, putting in and out of 4x4 and having my a/c switch vents. Came in and read your post. wow.