A/C issue
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New User
Joined: Mar 2004
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From: NE FL
A/C issue
I have a 99 F150 4X4 extended cab. Best truck I ever owned! The problem I am having is with the selector switch on the A/C. It is stuck on Defrost-Floor mode. The electrical is working; the unit will turn off/on. It just won't switch betwen Panel, Floor, etc. Any ideas?
Elder User
Joined: Feb 2004
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Most of the time its the blend door that cause problems. Check this thread
http://www.fordtrucks.com/forums/sho...threadid=24962
http://www.fordtrucks.com/forums/sho...threadid=24962
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New User
Joined: Mar 2004
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From: NE FL
Thanks for the info. I have heat and air. The problem is where the heat or air comes out. Do you know if this fix will work for the directional too (at least in princilpe)?
Thanks again for teh link. I'm still reading through the threads.
Thanks again for teh link. I'm still reading through the threads.
Hotshot
Joined: Aug 2002
Posts: 12,679
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From: BC, Canada
The discharge air location blend doors are vacuum controlled.
If you look up near the throttle pedal you can see the vacuum motors that control them. Check to make sure all the vacuum hoses are connected. You might also want to take a look at the back of the control to make sure the vacuum hoses are connected properly there too.
If you look up near the throttle pedal you can see the vacuum motors that control them. Check to make sure all the vacuum hoses are connected. You might also want to take a look at the back of the control to make sure the vacuum hoses are connected properly there too.
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Joined: Jun 2003
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Check the vacuum lines between the battery tray and firewall, especially the white ones, they tend to deteriorate (I think I spelled that right LOL) from the battery acid fumes and split or just plain turn to dust. There is a small vacuum resevoir mounted between the battery tray and the fender some times the hose comes off. There is also a large vacuum resevoir in behind the inner fender liner right front that falls of all the time. Loss of vacuum makes for an unhappy system. Defrost (I dont know about Defrost/Floor on your model) is the default mode for the system when you have a loss of vacuum so that the windshield will always be able to clear in icy conditions. If the actual switch (****) itself will not turn. You have a concern in the control head itself. You will have to replace the vacuum control switch itself.
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I have the same problem. It did it under warrenty and the deal said the replaced a check valve. That lasted untill it was out of warrenty. Strage thing is it comes and goes. Sometimes it works 10 percent the other 90 can't turn it
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New User
Joined: Mar 2004
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From: NE FL
Thanks all for the suggestions. I found the root-cause of the problem. The black vacuum hose near the battery is brittle and broke off at the connection. Does anyone have any ideas on replacing? It seems like it's going to be fairly difficult to replace due to the location.
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Pull the battery, then the battery tray out for better access. Just watch out for the vacuum tank attached to the tray on the fender side, it just snaps into the tray. As long as you dont need a long section of tube, you can purchase some windshield washer hose from your local parts store, about 5/32 I think and cut out the bad section of plastic tube and install hose over tubing. Ive done this many times before and it works OK. If its just where the tube goes into the rubber connector. Dig out the broken piece and reinsert whats left of tube into connector.
Last edited by Troll45; Mar 15, 2004 at 09:43 PM.
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New User
Joined: Mar 2004
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From: NE FL
The fix worked! I didn't have to go underneath the battery tray; as it turned out, the black hose was broke between the firewall and the connection just to the rear of the battery. I removed the connector and used the windshield washer hose directly, which worked well. Then slip over the existing black vacuum hose. It did not work until I cranked the engine...then, SCHA...ZAMMM, air came through the panel vents! I don't know what a "professional" would charge. But I know it would have been more than the .53 I spent on the windshield washer tubing. Thanks a bunch; this forum is awesome!
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Joined: Feb 2003
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Well I'll be. went and looked in the area ya were talking about and there is the check valve trh deal told me they replaced many mile ago. I removed it and did the blow test and it passed air both ways. I think you guys got me in the right direction 
Senior User
Joined: Jun 2003
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You can bypass all vacuum resevoirs temporarily to check the A/C. Just run straight manifold vacuum (At Idle) to the vac hose that goes into the passenger compartment for the A/C system. If the system still doesent work, the problem is in the passenger compartment. If it starts working the problem is in the engine compartment.