Hello, I have a 2004 f350 6.0. The ac was running fine and blowing out the vents and then all of the sudden it went off and started blowing out the defrost. I thought it was the relay under the dash so I switched it out and that didn’t help. I was driving and it came on and blew through the vents for a while then went off again. I thought it was the pump so I replaced it and that didn’t change anything either. I turn the key on and the pump runs continuously and never seems to turn off even when I have the ac off. Any ideas on what to check? Thank you

 

You have a vacuum leak somewhere. Do you have a 4x4 with ESOF? If so my guess is that doesn't work either. Vacuum leaks are a pain to locate.

 

Yes I do have 4x4 but I’m not sure what that other thing is. I haven’t tried my 4wd yet but I will tomorrow and we can see. Is there any diagrams that show the entire vacuumed system?

 

Take a look under the hood on the passenger side right behind the oil fill neck. You should see something that has 2 places a vacuum line can go on but it only uses one of them. It's real common for that vacuum line to come off.

 

There is a gray vaccine hose that’s just sitting in here but I’m not sure where it goes. There’s also a lot of air coming out around 2 lines I will take a video of it and post it. Other then that when I unhook the lines going to the thing for the 4wd and plug them off with my finger the pump never stops running. Same for when I plug it off going back behind the big box. The only time the pump stops running is when I unhook it from the vacuums box and plug it off, then it stops running. What does this mean?

 

It’s blowing air out of this spot. Is that normal?

 

If you give me a couple of hours I can take a picture and post it. There should be a round part about 1 1/4 of an inch round. There will be 2 spot to plug a vacuum line in. One will be on the top and one will be out of the front. When I knocked mine off I just plugged it into the one on the front and it fixed the problem.

 

That’s what I was thinking to. I plugged it in both holes and it didn’t change anything?

 

The vacuum system on these diesel trucks is super simple, much easier to follow than a gas engine. The vacuum pump pulls on the reservoir (big black tank next to the pump). It then connects to the HVAC system and the 4x4 system. That's it.

The HVAC is all in the cab except for the heater valve which is located on top of the engine, next to the turbo (I'm guessing that is the gray line you see disconnected). The vacuum pump cycles to maintain a certain level in the reservoir. If it's running continuously there's typically a leak somewhere in the system.

I would get a cheap hand vacuum pump and start pulling individual items into vacuum and you'll quickly find the source of the leak. Can be any number of things, split plastic lines, cracked reservoir, etc. The 4x4 system doesn't use vacuum continuously so it's probably not an issue there unless the solenoid is leaking. Typically if there are issues with the 4x4 it will go to defrost when you shift into 4x4.

Good luck!

PS, the leak you are pointing to in the photo is on the AC Evaporator box, you're feeling air from the HVAC system coming out. Turn off the fan and it should stop if you want to verify.