Vacuum issue?
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Mountain Pass
Joined: Aug 2007
Posts: 245
Likes: 3
From: Atlanta,Ga
Vacuum issue?
I have a 2004 Ex 4x4 with 131k miles that I purchased about 3 weeks ago. When I got it the AC would fail to the defrost mode when the 4x4 was on. I traced the problem to the ESOF valve and a cut line to the right hub. I replaced the valve and repaired the line and all was good. This past weekend I took the Ex on a road trip and discovered that under hard accleration the AC vents will fail to the defrost mode indicating a loss of vacuum. I made a quick check of lines under the hood and didn't find anything obvious. Is this a normal condition (I wouldn't think so)? If not, where is a good starting point? BTW my gas mileage was in line with what I've read on this forum (12ish) so it seems to be running OK.
Thanks,
Scott
Thanks,
Scott
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 423
From: Long Island USA
There is a vacuum reservoir which should keep vacuum in the heat/AC system, even under heavy acceleration.
You might have a cracked reservoir (which happens), a bad one-way valve (which I think is IN the reservoir) or even a leaky hose from the reservoir to the heat/AC system.
OR - a leaky diaphragm in the heat/AC system. Or the switch, or ...
To find the problem, disconnect the line to the AC system (I think it's on the firewall near the AC box under the hood) and put a vacuum tester on it - pump it up and see if it holds vacuum. If so, work backwards to the reservoir.
You might have a cracked reservoir (which happens), a bad one-way valve (which I think is IN the reservoir) or even a leaky hose from the reservoir to the heat/AC system.
OR - a leaky diaphragm in the heat/AC system. Or the switch, or ...
To find the problem, disconnect the line to the AC system (I think it's on the firewall near the AC box under the hood) and put a vacuum tester on it - pump it up and see if it holds vacuum. If so, work backwards to the reservoir.
Thread Starter
|
Mountain Pass
Joined: Aug 2007
Posts: 245
Likes: 3
From: Atlanta,Ga
There is a vacuum reservoir which should keep vacuum in the heat/AC system, even under heavy acceleration.
You might have a cracked reservoir (which happens), a bad one-way valve (which I think is IN the reservoir) or even a leaky hose from the reservoir to the heat/AC system.
OR - a leaky diaphragm in the heat/AC system. Or the switch, or ...
To find the problem, disconnect the line to the AC system (I think it's on the firewall near the AC box under the hood) and put a vacuum tester on it - pump it up and see if it holds vacuum. If so, work backwards to the reservoir.
You might have a cracked reservoir (which happens), a bad one-way valve (which I think is IN the reservoir) or even a leaky hose from the reservoir to the heat/AC system.
OR - a leaky diaphragm in the heat/AC system. Or the switch, or ...
To find the problem, disconnect the line to the AC system (I think it's on the firewall near the AC box under the hood) and put a vacuum tester on it - pump it up and see if it holds vacuum. If so, work backwards to the reservoir.
Thanks,
Scott
New User
Joined: Jul 2008
Posts: 1
Likes: 0
I have a 1999 F250SD, that was doing the same thing. i found that the 4X4 accuator was bad. mine is on the right side inner fender well right behind the vac tank. I unpluged the vac. lines and by passed the accuator and the problem was solved.No 4 wheel drive untill I replace it but its sumer and I don't really need it right now. Good luck and hope this helps.
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