2003 Ford F-150 Air Issue

  • 2003 FORD F-150
  • V8
  • 2WD
  • 146,000 MILES
When I use the normal air or the air conditioner feature and I speed up on the freeway, the air that is being blown from the front vents is forced to the defrost vents until I slow down to 50 miles per hour. The process also is done on the streets, any help on this issue is appreciated. Thank you
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have the same problem?
Tuesday, September 14th, 2010 AT 12:59 PM

1 Reply

See My Profile.

Imma CJ Jeep Guy.I have no A/C!

I can probably tell you what is happening, even though I do not know your particular vehicle.

I am a member just like you, Except I answer alot more. The Big Guys were "impressed?" With my knowledge. Even though I am not a professional mechanic. So I was given the title by my User Name.

What's a happening with yours is:

Your heater doors are OPERATED by vacuum (Using a VACUUM SWITCH in your Cockpit). Thats what makes them move. The wipers in my '46 Willys Jeep were Vacuum operated at one time. Back then the Mechanics of it were simple. Get on the gas, vacuum drops. Wipers slow down.

Since then things using vacuum systems have improved. One modification was the "Vacuum Resevoir" basically a Storage, per-say of Vacuum (large vessel with the air sucked out). This can provide that "Boost of vacuum" when Engine Manifold Vacuum starts dropping.

So we have a few things to look at, for the drop in your vacuum. Here are the ones I know---common to most vehicles:

1) Your engine is shot. And performance is terrible due to Mechanical Engine Wear and "GOOD" vacuum. Is impossible to achieve. This is the worst scenerio!

2) A vacuum line may be Off/ broke/ crimped/ SUCKING ITSELF FLAT because of deterieration. As was the case w/ a F-150 I repaired for a friend---of a friend. In front of his Throttle Body (this is his now) A really short hose was falling apart and sucking air. In a really tight spot, it was so bad you could hear it well!

3) A vacuum component (such as the resevoir, a "T", a connector, a switch, anything connected to vacuum!) Is Cracked/ broke off/ etc. . Some of these lines and components may be Encased in a "Wire Loom" etc.. Hard to find the leak.

4) You may have a component internally broke, thus not leaking vacuum. But Resticting fast flow thru a line. This would really be fun to find the traditional way, the way I usually search.

5) Your "Buddy" has swapped lines around, messing up intended operation!

OK, make a Search for something OBVIOUS now

Return with good news!

If none, I will explain other techniques to do a more advanced search.

Yes, Even I sometimes, have No Luck finding one.


The Medic
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Tuesday, September 14th, 2010 AT 4:01 PM

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