A/C will blow out defrost

2001 LINCOLN CONTINENTAL
1,770,160 MILES
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MICHAELDV
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when it gets 90% outside the A/C will start blowing out the defrost, it still blows cold. does it more when light on the gas when I have to down shift to clime hill it works fine. I changed the check valve and tested the vacuum can and it holds. is there something that I missing?
Aug 6, 2020 at 7:20 PM
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ASEMASTER6371
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Good morning,

This sounds like a vacuum issue.

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

I attached a flow chart for you below to do the testing. If all the vacuum system checks out, the control head is going to be the issue.

Roy
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Aug 7, 2020 at 4:43 AM
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MICHAELDV
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You know it's hard enough to fix this car but when you get a bad brand new part makes you go crazy. I guess that's why I don't have much hair left. I found that the check valve was bad. I had to wait for a hot day and hot engine to find the that the valve is bad. I really do not like working on car that are hot to find the problems.
Aug 7, 2020 at 9:48 AM
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ASEMASTER6371
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Good find.

I agree. You always assume the new part is good.

Roy
Aug 7, 2020 at 9:55 AM