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2002 F-350 4X4
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57 Posts
Discussion Starter #1
in my 2002, my ac works fine while driving in 2wd but when i turn the swith to 4 hi or low, my ac cuts off and it goes into defrost mode then about 2 mins later it returnes to normal. any ideas why this happens?
 

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Village Idiot
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8,209 Posts
You have a leak on your vac lines...prob small since your hubs are locking...
Or your not really in 4wd....chase the hard lines look at the connectors, up by the pump, and the lines near the tires. I had a line break by the front axel, year later a connector fail near pump..and my rubber lines jusr disintigrated into chewing gum.

A cu in plastic line can be spliced with a pice of rubber vacline. Same line fixed my rubber lines near tires.
 

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:whs: check the vacuum switch behind the passenger battery , plug off the line going to the hubs and see if your a/c works right and go from there. My factory hubs never worked right so mine stayed plugged off and i went with Warn hubs anyway.
 

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2002 F-350 4X4
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57 Posts
Discussion Starter #4
I checked out the lines and nothing looks messed up. So I locked the driver side wheel manually and the front drive shaft would not turn so I unlocked that wheel and locked the passenger side wheel but the front drive shaft would still move freely. Is there something wrong with the locking hub? also I just noticed when I but it into 4 low, the light on the dash does not turn on. What can this be. And thank you for the quick replys. I haven't had acces to the Internet latly
 

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I agree check the pvh solenoid on the right fender near the vacuum resivoir. These crack or fail internally and leak vacuum. It should be yellow in color and may have a crack in it. Plug off the line to it and see if the hvac works properly. I have replaced many of these for the same concern.
 

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2002 F-350 4X4
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57 Posts
Discussion Starter #6
i had a little time today to look at the truck. i pluged the lines going into the pvh solenoid and it fixed the problem of the ac switching into defrost. but i still have the problem that the "low range" light does not turn on when i switch in to 4 low. has anyone had this problem?
 

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If the transfer case is shifting into 4 low for sure then I would suspect a switch. Which is located on top of the transfer case, it threads in and is a two postion switch. I think when I replaced mine it was opposite for me, reg 4x4 light was not working but 4 low was. Very easy to replace, I think it cost around 70 dollars.
 

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2002 F-350 4X4
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57 Posts
Discussion Starter #8
Your saying it's just the light not turning on? How can I test it to see if it is engaging?
 

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When you turn the switch into 4x4 low are you in neutral, foot on the brake, and not moving. You will know if you are in 4x4 low, the transmission will shift fast and hard and your top speed is like 30mph. If it shifts into 4x4 low and the light does not come on then could be a switch that indicates the range I think, If not there may be other concerns as in shift motor or switch on the dash concern. I guess we have to know if it is actually entering 4x4 low. Let us know, Good luck
 

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2002 F-350 4X4
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57 Posts
Discussion Starter #10
I took some pictures so I can get a better idea as to which lines to work on:


^^ These are the lines going into the driver side tire, can someone tell me what each line is for?


^^ This line was eaten up at the tip so I cut it and plugged it back in. What is this line for??
 

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Top picture- left line is the vacuum line to the 4x4 hubs, middle line is your abs sensor wiring, right line is the brake fluid line to the caliper.
Bottom picture is your differential vent line.
Is the truck able to enter into 4x4 low? If regular 4x4 works then the hubs are locking in ok and I would not bother with that for now. I would concentrate on if low works and what is causing the light to not turn on. Hope this helps you out!
 
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