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Old 08-23-2011, 13:54   #1 (permalink)
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Defrost only club need help.. 98 4.6 f150

I have been doing tons and tons of research to find my problem and have done pretty much everything i can but still nothing.

The problem is the Air blows through the vents fine then under acceleration diverts to the dash.. From what i have seen on the internet is there is a vacuum leak.

All the functions on the knob settings work fine, (if i want to go from panel to floor ex.)

I took off the Climate controller box thing and disconnected the vacuum harness on it and was re-assured that there is vacuum coming to the controller (The middle black Hose). All the hoses have been replaced, PCV valve hose was replaced, and still nothing.

I also noticed awhile ago, when the last owner had the truck i remember having to put a ball of speaker wire inside the Vent door to keep the air from going to the defrost. Since then he had the Climate control box replaced and now that im looking at it, there are no more vent door things in the air duct. Could this be an issue?

Any help would be greatly appreciated, im just so confused about what my next step can be//

thanks
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Old 08-28-2011, 14:39   #2 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

Could it be the climate control unit?
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Old 08-28-2011, 17:14   #3 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

There's more than likely a vacuum leak in the system. It may be the check valve, reservoir, the lines or less likely, the controls and valve. They can cause the lak but first check all of the main circuit.
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Old 09-01-2011, 09:59   #4 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

Thats what i have been told and checked every line and replaced almost every one. As far as the reservoir, are you talking about the one thats under the fender with the four hoses or behind the battery? Those are even good and so are the hoses going to them.

I have plenty of vacuum coming into the cab and control unit, its just once i put the pedal about 1/4 to 1/2 way down while driving then thats when the air moves to the defrost.

I was looking around and someone said they had there climate control unit diagnosed by ford and it had a leak in it, He was also having the exact same problem as me, except i think he had an 03 with an electronic, and i have a manual, so i dont know if that make a difference in the diagnoses.

So I ended up buying a used one a few days again and it will be here today in about 5 hours.. Ill let you know if that doesnt work
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Old 09-01-2011, 21:18   #5 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

Check the vacuum after the engine is shut off, There should be vacuum for quite awhile in the lines. The reservoir and check valve help it to hold vacuum.
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Old 09-02-2011, 09:40   #6 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

When i turned the engine off it only comes through the dash for about 5 maybe 10 seconds with the settings on high.
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Old 09-06-2011, 13:59   #7 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

i pulled the check valve off of the brake booster with the truck off i heard air coming out of it, i assum this is a good thing?
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Old 09-06-2011, 14:16   #8 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

Quote:
Originally Posted by Jasenford89 View Post
i pulled the check valve off of the brake booster with the truck off i heard air coming out of it, i assum this is a good thing?
That would be normal .
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Old 09-06-2011, 14:32   #9 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

ok thats a good thing then. i know you havent really been in this thread but, is there anyway i can tell if the reservoir is bad?
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Old 09-06-2011, 18:15   #10 (permalink)
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Re: Defrost only club need help.. 98 4.6 f150

The booster isn't the reservoir for the HVAC system. Unplugthe line to the reservoir for the HVAC system.
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