Stuck on Defrost

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Sep 15, 2010 | 07:29 PM

jmgekeler

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From: Indianapolis, In

Stuck on Defrost

Hi all-

My heating system is stuck on defrost. I did some searching through the forums and found that I should check and replace the vacuum tube on the passenger side under the hood.

I did find a hole in the vacuum line, so I spliced in a new piece and still no luck.

What should be the next thing I check?

Thanks!
-Jason

Sep 15, 2010 | 07:52 PM

helifixer

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From: Chino Valley, Arizona

vacuum pump. do you have vacuum boost brakes or hydro boost? if you have vacuum boost and a pump failure you loose power brakes.

Sep 15, 2010 | 08:43 PM

jmgekeler

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From: Indianapolis, In

To tell you the truth, I am not sure, but I am going to say vacuum boost. That's what's standard on a 96 250 right? I do hear a hiss from under the dash when I step on the brake sometimes, usually when the truck is not running. Although I don't have any problems stopping.

Jason

Sep 16, 2010 | 12:10 AM

Talyn

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From: Ashland City, TN

pull the climate controls out of the dash, (carefully) and check the seals behind them to make sure its all sealed back there. sometimes they pop off, and you loose your vacuum.

Sep 16, 2010 | 08:14 AM

tbone heller

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From: Canton, Georgia

Using a hand held vacuum pump to apply vacuum to your dash line would answer a lot of questions.

Sep 16, 2010 | 09:23 AM

superduty4x4

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From: Newport, WA

Quote:

Originally Posted by tbone heller

Using a hand held vacuum pump to apply vacuum to your dash line would answer a lot of questions.

Yahtzee. Mityvac FTW.

Sep 16, 2010 | 12:56 PM

jmgekeler

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From: Indianapolis, In

So how does the system work anyway? I see the vacuum tube coming out of a wire bundle, which goes through the firewall. The tub is connected to what I think is some sort of actuator.

Does this actuator control the plenum? Should I be able to manipulate the actuator by hand?

thanks-
Jason