Vacuum Pump?
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New User
Joined: Jul 2004
Posts: 13
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From: Houston
Vacuum Pump?
I used my 4 wheel drive on Saturday. Since then, all my AC blows out the defrost. The AC is cold, just blowing out the defrost.
What could cause this? Is it easy to fix? How much?
What could cause this? Is it easy to fix? How much?
Fleet Mechanic
Joined: Feb 2004
Posts: 1,816
Likes: 3
From: River Valley AR
I don't know about your truck but lots of older vehicles use vacuum to operate the air doors. In the event that the vacuum source is lost, the doors would fail to the defrost position so you could at least still drive.
If your truck works like this you will have a vacuum line going into the firewall. Check for vacuum there, and maybe use a vacuum pump to apply vacuum.
If your truck works like this you will have a vacuum line going into the firewall. Check for vacuum there, and maybe use a vacuum pump to apply vacuum.
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New User
Joined: Jul 2004
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From: Houston
I think I isolated the problem. THe vacuum pump is running nonstop. The tube comes out of the pump and then goes into an oblong plastic box about the size of a nerf football. That seems to be where a leak is.
Do you know what this box is? It is right behind the battert (2 batteries on this truck)
Do you know what this box is? It is right behind the battert (2 batteries on this truck)
Fleet Mechanic
Joined: Feb 2004
Posts: 1,816
Likes: 3
From: River Valley AR
It may be an accumulator. Especially if it only has one line going to it. Think of it as a large volume of vacuum that is stored up. If you didn't have it you could only store up as much as the lines could hold.
Try to clamp the line that goes to the accumulator, them see if the the defrost problem straightens up. If it does, replace the accumulator.
As far as the vacuum pump running continuously, I think that's normal.
Try to clamp the line that goes to the accumulator, them see if the the defrost problem straightens up. If it does, replace the accumulator.
As far as the vacuum pump running continuously, I think that's normal.
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Thread Starter
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New User
Joined: Jul 2004
Posts: 13
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From: Houston
It has one line going in and one coming out. The one coming out powers the defrost and t's off going under the engine (Maybe transmission or 4wd).
I guess it is off to the shop tomorrow.
Thanks for helping
I guess it is off to the shop tomorrow.
Thanks for helping
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i have this same problem. my a/c works fine all the time except when i put it in 4wd. then the a/c defaults to defrost. the 4wd does not work unless you manually turn the hubs. the a/c quits whether the hubs are manually locked or not. i have no idea where the leak is though. the engine is much noisier than any vacuum leak. any tips on how to find the leak?
thanks, steven
thanks, steven