Hissing coming from dash

2001 FORD F-150
345,000 MILES • V8 • 4WD • AUTOMATIC
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IKEVINSCOTT
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When I am driving, there is a hiss coming from the dash around the heater control area, when I come to a stop, it goes away, and is not there when I idle. I find I have less power while driving, and again, seems fine while idling. I looked under the hood, and as far as i can see, from pictures i have found on the forums, everything is connected.
Before I take apart the dash, is there another way of diagnosing it?

I could get a replacement heater control from the wreckers for $50, which could be an easy job, if that is the quickest solution.

Kevin
May 22, 2011 at 5:24 PM
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IKEVINSCOTT
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I also noticed the a/c is always on, regardless of selector position. I disconnected the compressor, for now (unplugged the 2wire)
I also have exhaust I can see even on warm days (like winter exhaust)
May 22, 2011 at 5:32 PM
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FIXITMR
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sounds almost like a vacuum leak? so your exhaust is always steamy eve after warm up/driving? do you have to add any coolant once and a while?
May 22, 2011 at 8:58 PM
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IKEVINSCOTT
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After further inspection, the sound is like a leak, coming from the floor panel. The controls and the harness under the steering wheel seem fine
Maybe a vent control in there somewhere?
When I select vent or defrost, etc. The idle goes up and down slightly if that helps.

Coolant is always fine. The exhaust goes away after warm up
May 22, 2011 at 9:50 PM