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Old 01-13-2017, 03:42 PM
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Highway speeds and heater

Heater works fine at lower speeds (30's mph) but when i speed up to highway speeds (50+mph) my heat vents on the dash (above radio console and two door vents) cease to work. The windshield defroster still works however. Any thoughts on whats causing this? Recently replaced blower motor resistor to fix the full heat or nothing problem. Hoped it would have fixed this issue as well but did not.

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Old 01-13-2017, 04:01 PM   #2
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That's an odd one. So you have heat at highway speeds, but just those vents stop working? Does it switch to another vent when this happens or do you lose air completely until you select defrost?

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Old 01-13-2017, 04:41 PM   #3
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Check all of your vacuum lines that you were working around. Sounds like a blend door issue. You probably knocked one loose or it has degraded
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Old 01-13-2017, 04:59 PM   #4
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Originally Posted by rednblues View Post
Check all of your vacuum lines that you were working around. Sounds like a blend door issue. You probably knocked one loose or it has degraded
Yep likely vacuum lines.
Default is defrost, so sounds like you are losing vacuum somewhere feeding the dash controls.
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Old 01-13-2017, 06:09 PM   #5
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If it is defaulting to defrost only when you have low engine vacuum like accelerating or going up a hill, the hose is probably cracked or off at the vacuum reservoir in the fender well under the battery. If not, it is possible you have a bad check valve in the line between the intake manifold & the T above the battery where the line splits to go to the reservoir & into the cab.
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Old 01-13-2017, 06:10 PM
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Sounds like a good place to start ill check vacuum lines tomorrow. Appreciated.

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Old 01-13-2017, 11:56 PM   #7
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Sounds like a blend door issue.
No.
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Old 01-15-2017, 12:59 AM   #8
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No.
No what?
That's not helping the guy...
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Old 01-15-2017, 08:53 AM   #9
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It is a vacuum leak or failed check valve in under hood vacuum hose

Find and fix

Giveaway is happens with TB open and works right at idle when engine makes lots of vacuum


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Old 01-16-2017, 09:31 AM   #10
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No what?
That's not helping the guy...
Blend door controls temperature of the air buy moving air to or bypassing the heater core.
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Old 01-18-2017, 12:03 AM   #11
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yeah, I know. I wasn't paying attention when I posted. I think he got the point...Apparently the other guy didn't. hence the NO, which was rude.

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