Truck A/C changes to defrost when accelerating

**jmw_man** · 06-25-09, 10:15 AM

So the title pretty much says it all. Most likely I have a vacuum leak somewhere though I just don't know where to look.

It's a 2001 Ford F-150 XL fleet truck with 165000 miles on it.

This just started happening about a week or two ago and I have noticed it getting a bit worse. It started switching to defrost or the floor (one of the two) when accelerating uphill, now it does it pretty much any time I'm accelerating.... Thoughts?

**BruceBloodMaster** · 06-25-09, 10:22 AM

Sounds like the switch in the dashboard may be bad. If it was a vacuum leak you would hear it and the truck would run Different. However if the switch is bad there wouldn't be any noise. My thought is check the switch. Hope this helps JMW

**jmw_man** · 06-25-09, 10:24 AM

The switch was my first thought.

Co-workers of mine swear I have a vacuum leak, I honestly don't know much about it so I'll have to look into both. Thanks for the tip.

**BruceBloodMaster** · 06-25-09, 10:26 AM

Its probably the switch because as you accelerate the vacuum decreases and the switch may be moving due to the lack of vacuum

**ALPINESTAR** · 06-25-09, 11:56 AM

its electrical, otherwise the vacuum line would cause it to stay defrost all the time

**jmw_man** · 06-25-09, 12:26 PM

Originally Posted by ALPINESTAR

its electrical, otherwise the vacuum line would cause it to stay defrost all the time

I can see what you are saying, though, when you are accelerating you are drawing more horsepower away from the A/C so don't you think it's possible that the vacuum leak could be caused while accelerating?

**BigHub** · 06-25-09, 01:01 PM

Good thing mine blows snow 24/7... Truck ends up being a freezer, even if it's 120 degrees out.

**RagunCajun** · 06-25-09, 01:12 PM

I had a similar issue with a car once, turned out to be a $ 2.00 check valve on the vacuum line under the hood.

**ALPINESTAR** · 06-25-09, 02:03 PM

Its possible, I would try just seeing if anyone has had similar problems on some Ford forums maybe.. Anytime I can't figure something out I google the phrase and get some good hits.

**jmw_man** · 06-25-09, 02:10 PM

Originally Posted by ALPINESTAR

Its possible, I would try just seeing if anyone has had similar problems on some Ford forums maybe.. Anytime I can't figure something out I google the phrase and get some good hits.

The trick is coming up with the best phrase, this one is actually kind of hard....

I did google one but I didn't have the best of results.