heater works great but it will not blow through the defrost vents?

1986 FORD F-150
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MWJW27
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Heater problem
1986 Ford F150 V8 Two Wheel Drive Automatic

'85 ford f-150. the heater works great but it will not blow through the defrost vents. it just keeps blowing through the dash vents. is there a door that's not closing or some vacuum problem?
Nov 15, 2008 at 7:33 PM
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DAVE H
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I would check under the hood for broken vacuum lines headed inside the cab. THis guide can help plus I have found the HVAC vacuum line diagram so you can make sure all points are getting vacuum.

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

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Nov 16, 2008 at 8:42 AM
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