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Old 12-19-2015, 09:40 PM   #1
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Join Date: Dec 2015
Location: Midlothian, Tx.
Posts: 132
Ford E series AC vent vacuum fix

Many of the Ford vans have a problem with the ac vents not working or defaulting to the defrost vents when on ac or heat. Mine is a 1999 E450 but the E350 as well as the 450's used for C class motor homes and the F150's all have the same issue. The vacuum accumulator and check valve are located between the fender well plastic on the right hand side and the battery in a space inaccessible without removing the fender and the plastic behind it. The common fix is to run the red vacuum line off the tee on the rear of the motor that comes across the right side right above the battery directly to the ac vacuum line at the right side under the dash in front of the passenger seat, this bypasses the bad accumulator, check valve or cracked line inside the fender you can't get to. When you bypass all that the vents all work till you try to pass a car of go up a hill and the engine vacuum drops, the dash vents close till you let off the gas and the engine vacuum builds back up.

a check valve, a sealed tank of some sort and a T to fit the small lines are all the parts required to fix it. I used a 134A can drilled on the top and tapped to 1/8th npt to fit a 1/8th npt x 3/16 fitting screwed and lock-tighted into the top.

The check valve goes to the red vacuum line over the battery, the Tee goes to the home made vacuum accumulator, the other side of the check valve and the line to the dash. The check valve lets the accumulator hold vacuum when the engine vacuum falls. The tank holds it's vacuum and the vent doors in place till the engine regains vacuum.
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CharlieD is offline   Reply With Quote
Old 12-20-2015, 07:06 AM   #2
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Join Date: Mar 2014
Location: Beautiful West-Central Florida
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The problem happened to me Charlie, and it cost me about $1000 (mostly labor) for the Ford dealer to repair. I wish I would have known about your fix before that.

2012 Greyhawk 31DS
2012 Ford Edge Toad

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Old 12-20-2015, 11:37 AM   #3
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Join Date: Dec 2015
Location: Midlothian, Tx.
Posts: 132
It's crazy Ford couldn't find a accessible place for the Reservoir and check valve. If I was over their Engineering group, whoever approved that design would be in another job.

Dorman makes a couple of plastic reservoirs but none were in stock in my town, the used 134a refrigerant can was in my shop trash can and it fits between the battery and radiator with a zip tie. I had some thick felt to wrap it in so it wouldn't rub on anything.
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