AC fan switch problems! Please help!!

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Aug 25, 2013 | 05:49 PM

Supper Duddy

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AC fan switch problems! Please help!!

I have a 99 F350 Super Duty V10. The fan vent only blows out air on the defrost setting. It also seems to blow out of the center vents when I'm driving on the highway and let off on the gas and slow down. If I'm under load or on the gas the fan will only blow out the defrost, no matter which setting the fan switch is on. Also, it seems that when I have the selector switch on the vent, the AC is running. I pulled the plug wire to the compressor and tested it and I have power when I have the switch on AC. When I turn the fan switch to vent I still have power at the plug.
Anyone have this problem or know what I can check to fix it? I don't want the AC running in the Winter when I need to use the heat!
Thanks,
Supper Duddy

Aug 25, 2013 | 05:58 PM

Hotpocket

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From: Needville, TX

vaccum leak...check your 4x4 hubs first if you have an auto 4x4 system

Aug 25, 2013 | 07:29 PM

Supper Duddy

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Quote:

Originally Posted by Hotpocket

vaccum leak...check your 4x4 hubs first if you have an auto 4x4 system

Why at the 4x4 hubs??

I checked the vacuum lines under the hood at the firewall and couldn't see any problems. Does anyone have a diagram of the vacuum lines? So I can go through and check them all?

Aug 26, 2013 | 06:46 PM

projectSHO89

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From: St Louis

If you have 4 x 4, check the PVH solenoid. It's a common leaker.

Aug 26, 2013 | 08:13 PM

redford

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From: Stephensville WI

The heat/AC system is vacuum powered. If there is insufficient vacuum to run the system, it blows through the defrost vents by default.

The automatic 4 wheel drive hubs were suggested as a starting point, but any vacuum leak will cause your issue.

Aug 26, 2013 | 08:48 PM

Supper Duddy

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Thanks for the replies! I was looking on youtube and think I may try to "smoke" out the vacuum leaks. I don't have a smoker, but saw how you can make your own with a coffee can and cigar.
I'll let you know how it goes!

Aug 29, 2013 | 10:13 AM

Supper Duddy

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I did the cigar test and found a lot of smoke leaking from the PVH Solenoid. The dealer wants $83 for one. I found them on ebay for $60 but it says they are for auto locking hubs. My hubs are manual locking at the wheels, but I have a switch on the dash to switch into 4H or 4L or 2H. I researched it and found that this is an override switch to the lockout hubs. So do I have AT hubs or Manual?
Do I need to buy a whole new solenoid or just change out the hoses? I saw it leaking at the electrical connection, but not sure if that was the only place, cause smoke was all over that box! Also, I don't have any problems with my 4x4. I put it in 4x4 and turned on the vent and it came out of the vent it was set at. I could get air at the floor and center vents, as well as defrost.
Any suggestions would be helpful as I would like to get this fan problem fixed before the Winter!
Thanks!