AC switches to dash when in 4x4?

[orion_134]

My ac works perfectly, unless I switch the dash selector into 4hi or 4lo...then it kicks off the vents and to the windshield in defrost, almost like it has lost all of it's vacuum...as if the 4x selector is cutting the vacuum from the ac selector.
Any thoughts or ways I can test it?
Jesse

 

[oi8228oi]

diesels dont have vacume... but thats all i can help you with

 

[Ford_Forgotton]

Diesels *DO* have vacuum!

Its called a vacuum pump, and its on the passenger side fenderwell. It controls your AC vent doors, and your 4x4 automatic hubs.

WHat happens is (typically) the 4x4 vacuum lines ROT and leak. You will lose 4x4 actuation, and you will get your AC out the windshield.

Check the back side of your wheels and you will see a rubber line that is all cracked and weather checked and maybe even broken.

Fix that, and you'll fix your AC

 

[oi8228oi]

see that you learn something new every day

 

[Ford_Forgotton]

Seriously tho, diesels do in fact have vacuum, or else they wouldnt start. The only exception to this were some 2-stroke diesels that had a crank driven blower to force air into the cylinders during startup. Some even had turbo/supercharger combos!

The difference between gasser vacuum and diesel vacuum, is there is no thottle plate in a diesel. Therefore there is nothing to draw a measurable vacuum against. A diesel just draws in what it needs without anything in the way to prevent air from getting in.

But thats all just education and has nothing to do with the problem he is having per say. Net effect, is for a reliable source of vacuum in a diesel application, an electric or mechanical vacuum pump is installed to provide the vacuum needed to operate various piece of equipment.

 

[threejacks]

If your rubber lines are rotted or broken this is what fixed my son's 2000 PSD. http://www.dieselsite.com/index.asp?PageAction=VIEWPROD&ProdID=348
What you have is a safety issue. Even with bad lines you will always have defrost.

 

[orion_134]

Do you think the bad lines are all the way outside the truck instead of behind the dash? Or are you saying a leak in one place will not let the vacuum supply be great enough to power both the hubs and the ac?
Jesse

 

[threejacks]

The rubber lines that go from the frame of your truck to the 4X4 hubs can get cracks in them and all your vacuum air goes out of them. Your defrost kicks in as a safety factor. This is not a high pressure amount of air, yes it will leak out outside your truck and cause it to happen. Your systems are exactly the same as several others have experienced and the cure to the problem was new lines. The ones from above are stainless steel braided and work a lot better than OEM and from what I found were cheaper than OEM prices.

 

[orion_134]

Ordered them yesterday along with the Fumutomowhatever drain valve.
Thanks guys, now to fix my VSS error...
Jesse

 

[orion_134]

Well, installed the braided lines with plenty of thread tape and still have the problem...help?

Also, should my hubs say "lock" and "auto"? One says "free" and "lock", and one says nothing...they obviously have been replaced, but I am trying to figure out if they were replaced with the correct parts and approx. how long ago...
Jesse