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Discussion Starter · #1 ·
I just purchased a used 2005 Powerstroke Lariat crew cab, love it and have some cool mods on tap. But driving it home I noticed that the AC was stuck in the Defrost mode. It started raining and got cooler and all of the sudden the AC started working correctly. It works correctly until I turn the AC off, then turn it back on. Then it takes a while (two hours or so) to get off of the defrost..

Second thing, I think my hubs are stuck in the locked on position. When I shift it to the 4x4 position the truck goes into four wheel drive but there is no audible sounds or anything, unlike in my Chevy. When I turn it back to two wheel drive, it goes back into two wheel drive, but there is no sounds of disengagement or anything.

After looking over the forum I think that it is something with the vacuum pump. What do you guys think? Great forum guys.
 

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You need to check the vaccuum lines at the pump. Do a vaccuum test with a mighty vac hand held vaccuum pump. If it does not hold vaccuum then you have a leak on that line.

Your a/c problem can be caused by the hubs. But you need to test the system before you start tearing things apart.

Sometimes the hubs will make a noise and sometimes they won't. What you can do is put the trans in neutral. Jack up the truck block the rear tires so the truck. Then turn the front tires by hand. Watch the front driveshaft see if it turns.



I forgot the vaccuum pump is located on the passenger side of the engine compartment behind the battery on the passenger side wheel well.
 

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Discussion Starter · #3 ·
Thanks for the input, Just some additional info. I have noticed that it only happens when it is really hot and I turn the ac off then back on or if I turn the truck off and then back on quickly. The reason that I was looking at the hubs is that when this happens the mpg on the computer fall quick, like will go from 14 to 12 in minutes then come back fairly quickly when everything straightens out.

I have visually checked the lines and they look ok. I put vacuum on the only hose that I have coming from the pump and it holds vacuum.

The pump acts squirly though. I pulled the line off once and the pump kicked on for like one second and shut down. It hasn't repeated that trick again. I took the electric plug off to inspect for a worn wire and the pump wouldn't stop when I plugged it back in until I shut the truck down. When I started it up, nothing from the pump but the ac was working right.

My Grey line looks like it is out of place I have reattached it but it looks like it is improperly routed. Don't know if this has anything to do with it but??

I don't know the proper troubleshooting steps to test the pump. I have a service manual coming but would like to get a jump on it if possible. Anybody know the steps?
 

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i have a similar problem ac blows out of the defrost vent after 4x4 is engaged then returns to normal. my upper and lower ball joints were replaced at the dealer, this is when it started ,they might have damaged the lines to my hubs,this is all i can come up with. i need some help also.
 

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Discussion Starter · #6 ·
Ernie I am by far away from an expert on this stuff but I hunted first for a leak in the vac system. Other than some routing issues I couldn't find a leak. I figured out that if I hit the motor it would turn on the pump and then it would work. I put a new one in and everything is working fine. I am hoping there is not an itermentent leak and it doesn't just burn out the pump. Time will tell.
 

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have your fan sensor checked. we had the same problem are ac and defrost would act up and byreplacing the sensor everything went back to normal. no clue on your hubs though sorry :(. just a question what do u meen by an audible sound
 
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