stuck on defrost
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Joined: Jul 2010
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stuck on defrost
my 03 f250 super duty is stuck on defrost. i have looked at vaccum lines and they seem to be fine. i did find an electrical plug unplugged on the vaccum pump on the passenger side inner fender. i believe that it is to the 4x4 lockers. i just bought the truck and know nothing about it. any info would be great.
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
The air direction doors in the HVAC are operated by vacuum. You most likely have a bad vacuum pump or a big vacuum leak.
First off, is your pump running? If you disconnect the hose from it does it run? If not, it's probably bad.
If it does run, disconnect the hose from it and put your finger over the nipple. The pump should stop running almost immediately. Again if it doesn't it's probably bad. If it does, then it's OK and you have a leak.
Then you need to start working your way down the lines, one at a time. Removing them and plugging them off and waiting to see if vacuum builds. Eventually you should get to the point where vacuum won't build and you will have isolated the bad line.
First off, is your pump running? If you disconnect the hose from it does it run? If not, it's probably bad.
If it does run, disconnect the hose from it and put your finger over the nipple. The pump should stop running almost immediately. Again if it doesn't it's probably bad. If it does, then it's OK and you have a leak.
Then you need to start working your way down the lines, one at a time. Removing them and plugging them off and waiting to see if vacuum builds. Eventually you should get to the point where vacuum won't build and you will have isolated the bad line.
Postmaster
Joined: Apr 2006
Posts: 3,524
Likes: 2
From: CA Bay Area
Most common problem on 4x4 are leaky vacuum activators. From what I read on this forum, since mine is 2WD.
I have electric glitch on my pump control. Sometimes it works, sometimes not, sometimes it start working after bump on the road. Having no electrical diagram, I don't know where to look so I made a jump wire parallel to the hot wire at the pump. When I want it to work, I just attach the wire to battery terminal.
I have electric glitch on my pump control. Sometimes it works, sometimes not, sometimes it start working after bump on the road. Having no electrical diagram, I don't know where to look so I made a jump wire parallel to the hot wire at the pump. When I want it to work, I just attach the wire to battery terminal.
Elder User
Joined: Dec 2008
Posts: 745
Likes: 4
From: North Carolina
I know the OP said he had a vacuum pump but the statement "electrical plug unplugged on the vaccum pump on the passenger side inner fender. i believe that it is to the 4x4 lockers. " made me wonder.
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