air direction selector
Cargo Master
Joined: Feb 2011
Posts: 3,450
Likes: 13
From: Forest lake minnesota
Most likely you have a vacume leak somewhere , when the system loses vacume it defaults to the defrost position. If its a diesel it could be the vacume pump. A gasser going to be a line somewhere.
Cargo Master
Joined: Feb 2011
Posts: 3,450
Likes: 13
From: Forest lake minnesota
I dont have a diesel but I think its on the drivers side front fender. Do a search on the forum and you should find lots of info on it. Otherwise I am sure a diesel guy will be along shortly to help as well.
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
Start by checking the two wire connector to the vacuum pump. One wire should be ground and the other should be hot when the key is on.
Then take the vacuum line off of the vacuum pump (with the key on). It should run. Put your finger over the nipple and it should shut off. Reconnect that line, follow it down and do it again. Pump should shut off again. Repeat following down the lines. Once you get past the vacuum resevoir, it will take a few minutes for the pump to pull a full vacuum but it should eventually shut off.
There is a T connector on top of the vacuum resvoir, on of the lines goes back into the cab for the heater controls, one goes forward to the PVH (Pulse Vacuum Hublock) solenoid, if you have 4WD.
If you haven't found a problem by this point, come back and we'll go further.
Then take the vacuum line off of the vacuum pump (with the key on). It should run. Put your finger over the nipple and it should shut off. Reconnect that line, follow it down and do it again. Pump should shut off again. Repeat following down the lines. Once you get past the vacuum resevoir, it will take a few minutes for the pump to pull a full vacuum but it should eventually shut off.
There is a T connector on top of the vacuum resvoir, on of the lines goes back into the cab for the heater controls, one goes forward to the PVH (Pulse Vacuum Hublock) solenoid, if you have 4WD.
If you haven't found a problem by this point, come back and we'll go further.
Post Fiend
Joined: Feb 2007
Posts: 5,078
Likes: 0
From: Rural WV
Thought my vac pump was bad too...in fact I had already started looking at replacement prices. Turns out my PVH valve was bad. It was all cracked. I ordered the part (FYI it's 7C3Z-9H465-A) and it cost me less than $100 so it's a relatively inexpensive repair.
Joe
Joe
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