The dreaded Ford A/C default to defroster conundrum

[Jb1rd]

I bought the van with full knowledge that the A/C (which does blow nice and cold, just not where I want it to) was only blowing through the defroster vents, foolishly I thought that it would be a simple fix, WRONG!! After watching several YouTube vids and reading more than a few forum posts, I have successfully destroyed what is left of my brain trying to find the vacuum leak causing the problem, no luck as of yet but I am determined to figure it out. There is a pump that might be bad but I'm unsure how to use my fancy volt meter to find out for sure. I am lucky enough to have a life long family friend who is an to goodness, awesome mechanic that is always a phone call away and even better yet only 30 minutes down the road. I am hoping that with his help I will have this sorted out before my shake down trip on the 5th!! I will do my best to remember to take pictures and report back what I find. FWIW most of the videos and the forum posts I have consulted seem to think that the control module in the dash is the least likely culprit, I will try to confirm this as well, and most people seem to find the problem is related to the condenser which is apparently not very easy to get to so they run a "jumper" line/ hose from the intake and bypass the condenser, however, I'm not sure if that has any long term repercussions.

 

[villageidiot327]

If it blows cold, then the condenser is doing its job.

If you have air coming out of the dash in the defrost ducts, but nothing from the dash ducts, I'd look to the flap that controls the direction of flow. Sometimes the little door breaks, sometimes the vacuum pod is bad.

I'm not sure how bypassing the condenser will change the output of your air.

Good luck and all that.

 

[4x4pair]

On mine the vacuum "tank" that holds the pressure went bad. It's practically impossible to get to so I bypassed it using a small vacuum tank I found on Amazon and some vacuum tube. Works great now.

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[brianjwilson]

On mine the vacuum "tank" that holds the pressure went bad. It's practically impossible to get to so I bypassed it using a small vacuum tank I found on Amazon and some vacuum tube. Works great now.

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More details please! I meant to start a thread on this too. Mine switches to the defroster under near full throttle, then returns to normal after a few seconds. Small vacuum leak? Check valve?

 

[IdaSHO]

More than likely nothing more than a vac leak.

Also, keep in mind that if its diesel, you very well could have a bad or going-bad vacuum pump.

Silly diesels don't have throttle plates, so they do not create their own manifold vacuum.

 

[86scotty]

On mine the vacuum "tank" that holds the pressure went bad. It's practically impossible to get to so I bypassed it using a small vacuum tank I found on Amazon and some vacuum tube. Works great now.

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Ding Ding Ding Ding Ding! This is what it is. Most Ford vans do it eventually. I just bought a 2005 V10 with only 30k and it's already doing it. There are lots of posts and info on this on the Sportsmobile forum and on Ford Trucks (FTE) forums. JWA (username at either of those) has posted a lot about it and linked some videos.

Good luck! I'd definitely add a vacuum canister somewhere first. That'll probably be about $2 from a salvage yard.

 

[hobietony]

I had the issue. there is a vacuum tube that runs from under the hood through all kinds of non-removable plastic stuff. Mech suggested a re-route via a less intrusive path - I actually ran it out the engine compartment, behind the fender, and back in through the opening for the wires/cables to the door. pretty easy

 

[4x4pair]

I used this $13 canister from Amazon: Dorman 47077 Vacuum Storage Canister. Then I ran tubing through the passenger side firewall up underneath the dash to where that little access panel on top of the dash is and connected it.

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[hooptytank]

On my f250, the hard white vacuum tube had disintegrated. On the trucks, it's by the firewall next to where the heater hoses enter the cab. Cut the tube and slipped a piece of vacuum hose to make connections.

Not sure how the vans are laid out, but look for any damage to the hard plastic vacuum hoses, especially underhood where they're exposed to heat and chemicals. Feel them with your hand the whole length, sometimes the damage is not visible, but you'll feel it. Good luck

 

[Bikersmurf]

You were correct that it'll be a simple fix... Finding the problem is what's hard

Good luck with your search... I've got all the heater boxes and ducts sitting in the parts pile if a pic of something if it'd help. Unfortunately, I've stripped most of the vacuum lines off already.

 

[VOODOO7.3]

Jb1rd, what engine is in your Ford? Most likely culprit is a hidden vac hose T connection to the vacuum reservoir tank, which is directly above your front passenger side inner wheel well at 12 o'clock. If you are lucky enough to have a diesel, you don't need a tank at all. All you need to do is run @ 8' of vacuum hose from center dash access panel to vacuum splitter under hood. For gasser, I would consider cutting a 3" X 5" access hole in top of inner fender, fix hose and connections to reservoir, and make new access cover plate, as outlined in other forums. Good luck!