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Old August 28th, 2007, 05:02 PM   #1
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Default HVAC switches to defrost under load.

Here's my other issue on my truck ('01 Dodge Ram 4x4).

Say I have the A/C pointing at my face. If I'm on the freeway and give it 3/4 throttle so the load increases on the engine, the vacuum change causes my HVAC to switch to defrost.

I've checked with tech manuals and it is supposedly a common problem says to replace both check valves on the vac lines near the intake manifold.

I pulled both valves and checked them and they hold vacuum. The lines don't seem to have any leaks either.

Any help?
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Old August 28th, 2007, 07:11 PM   #2
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Ask PP he knows everything.
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Old August 28th, 2007, 09:36 PM   #3
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Ask PP he knows everything.
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Old August 28th, 2007, 09:38 PM   #4
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is there a vac res to hold vacuum to the hvac under at wot?
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Old August 28th, 2007, 09:49 PM   #5
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your truck just wants to make sure you have a clear view when going that fast
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Old August 28th, 2007, 10:39 PM   #6
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is there a vac res to hold vacuum to the hvac under at wot?
Not that I can see. I'll have to pull up some diagrams tomorrow in the auto building computer lab and see if there's anything.
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Old August 29th, 2007, 11:25 PM   #7
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Usually it means the res is cracked, or disconnected.
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Old August 29th, 2007, 11:40 PM   #8
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Usually it means the res is cracked, or disconnected.
Where's the res located?
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Old August 30th, 2007, 08:21 AM   #9
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Hmm, my 96 ram does it also, its really annoying..

Hoping muddypaws will post some purty diagrams....

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