Goes to defrost

Tiny
TIMOTHY HARGERS
  • MEMBER
  • 2002 FORD F-150
  • 280,000 MILES
When I accelerate with my air conditioner on the AC doesn't blow the same
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Tuesday, August 30th, 2016 AT 1:44 PM

3 Replies

Tiny
WRENCHER1
  • MEMBER
It is switching to defrost.

The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.
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Monday, April 19th, 2021 AT 3:02 PM
Tiny
TIMOTHY HARGERS
  • MEMBER
Thank you so much I will look for it.
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Monday, April 19th, 2021 AT 3:02 PM
Tiny
KEN
  • ADMIN
Here is a guide that can show you what to look for:

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

Please let us know what you find so it will help others.

Best, Ken
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Monday, April 19th, 2021 AT 3:02 PM

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