HBJJAM
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• Minneapolis, MN, USA |
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• Registered on 6/23/2005 |
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• 93 posts |
• 1
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 Posted:7/16/2010 04:53 |
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I know I have a leak 'somewhere' since when ever I have the A/C on that dash vents will fluctuate between the front vents and the defrost 
Really stinks when the outside temp is up like this past week.
What is the census on the best way to troubleshoot a leaking vacuum?
Anyone else have or had this and found maybe a particular area or componet that is more sustable to failure?
There are so many damn lines that it is hard to her this leak.
Btw, it is a 2000 V10 with aprox 109,000 on the dial.
thanks 
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LANDYOT
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• Subscriber since 11/23/2003 |
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• Newport News, VA, USA |
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• Registered on 7/15/2003 |
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• 1,110 posts |
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Posted:7/16/2010 12:45 |
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My first guess would be the lines that service the locking hubs (assuming yours is 4WD).
I've known a couple folks who replaced all of the vacuum lines on a couple cars (not Excursions), and they both commented that the car "felt" much better afterwards. It might be time for yours. |
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HBJJAM
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• Minneapolis, MN, USA |
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• Registered on 6/23/2005 |
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• 93 posts |
• 1
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Posted:4/8/2011 16:36 |
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YEA well this is still an issue
I have done all the testing I can find and am still coming up short!
I removed the vac res and just ran the lines together, at least doing this kept the vent control out the dash until i floored it on the test drive.
anything over 65mph or 22rpm also lost the vent to defrost direction
I am at a loss of what i am chasing.
I am starting to think it is more into the a/c controls then anything else
anyone have other ideas? |
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dnevins
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• Subscriber since 12/29/2009 |
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• San Diego, CA, USA |
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• Registered on 12/28/2009 |
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• 340 posts |
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HBJJAM, the test you did with the reservoir actually tells you a lot. On these vacuum-controlled Ford heater/A/C systems, defrost is the fail-safe: when the mode doors lose vacuum, the system falls to defrost so you can always clear the windshield. Engine vacuum drops to almost nothing when you floor it, and it gets weak under a hard pull at highway speed. The vacuum reservoir and its one-way check valve exist to hold vacuum for the dash through exactly those moments.
When you took the reservoir out and joined the lines, you took away the stored vacuum that carries the dash through a long low-vacuum stretch. If the check valve came out with it, the dash vacuum now just follows engine vacuum. Either way, dropping to defrost when you floor it or run over 65 is expected with that setup. The fact that it behaved better at cruise with the reservoir gone points at the reservoir or its check valve leaking.
What I would do:
1. Put a new reservoir and check valve back in the supply line. Test the check valve before it goes in: blow and suck through it. Air should pass one way only. If it passes both ways, it is bad.
2. With a hand vacuum pump, pull vacuum on the supply line going into the cab, engine off, and watch the gauge. A tight system holds steady. If it bleeds down, the leak is on the dash side.
3. If it bleeds down, move the selector through each position while watching the gauge. A leak in only one mode points at that door's actuator or its hose. A leak in every position points at the vacuum selector valve behind the control head (they can break internally) or the main supply line through the firewall.
For anyone who finds this later with the same symptom: the usual cause is the vacuum supply side (check valve, reservoir or a cracked line), not the A/C electronics.
Dana
https://partslogic.com |
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