2002 Ford F150 Heat or A/C will not switch from defrost, pa

2002 FORD F-150
160,000 MILES • V8 • 4WD • AUTOMATIC
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RONB3244
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Most of the time my heater or A/C will only blow out of the dash board (defrost) vents. If I choose Panel/Floor it will sometimes switch if I'm going down hill with my foot off of the accelerator. When I am accelerating it switches to blowing out of the defrost vents. So, under load it seems as though it will only blow out of the dashboard vents. Do you know what is going on?
Feb 17, 2010 at 4:12 AM
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2CARPRO JACK
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Closely inspect ehvacuum lines that run between thebattery and firewall.I have seen a bunch of those rot out the vacuum line from the battery acid.Low/no vacuum will do exactly what you describe
Feb 17, 2010 at 9:02 AM
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RONB3244
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Thank you for the prompt reply. Sorry for my ignorance, can you describe what vacuum lines look like? How thick are they? What material are they made of. Thanks for your help.
Feb 18, 2010 at 5:28 AM
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2CARPRO JACK
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  • 11,533 POSTS
They are small black plastic hoses that run between the battery and firewall on the passenger side, approx 1/8 inch
Feb 18, 2010 at 11:39 AM
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