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Old 02-08-2008, 11:38 AM   #1
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Default How easy it is the change the blend door?

On the general board I have documented my problems with the heat in my truck. It gets warm, but not good and warm. The thermostat is brand new. I believe it is the blend door because when the heat first comes on if I have it set to vent, nice hot air blows out for a couple of seconds, then there is a dull thump sound back in the dash and the air cools to lukewarm.


So how easy of a fix is this on a 94 regular cab?
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Old 02-08-2008, 03:59 PM   #2
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Have you checked all your vacuum lines? I had a similar problem and found out it was a leaking vacuum line. You can find them in a cluster inside engine compartment on the firewall on the pax side. Mine were made of vinyl and the vinyl cracked and began sucking air. I had the cracked piece spliced with rubber tubing and it worked like a charm. The blend door is move by vacuum. When you lose vacuum the door doesn't open or close fully.
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Old 02-09-2008, 10:20 AM   #3
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I agree with you, buck8200, it is probably a vacuum problem, not a blend door problem. I have seen very few blend doors, or even distribution doors actually go bad. It is usually the controls. The give away to me is the 'thump'. I would also check the vacuum tree on the firewall, the vacuum cannister, looks like a big soup can, and all the vacuum lines. Sometimes if all is quiet with the engine running, and moving the selector switch while listening, a vacuum leak can be heard.

Good luck on the repair, and let us know what you find.

Dan Harriman 84 F150 lwb
Orange, Texas
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Old 10-03-2008, 03:27 PM   #4
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Originally Posted by kc5gxl View Post
I agree with you, buck8200, it is probably a vacuum problem, not a blend door problem. I have seen very few blend doors, or even distribution doors actually go bad. It is usually the controls. The give away to me is the 'thump'. I would also check the vacuum tree on the firewall, the vacuum cannister, looks like a big soup can, and all the vacuum lines. Sometimes if all is quiet with the engine running, and moving the selector switch while listening, a vacuum leak can be heard.

Good luck on the repair, and let us know what you find.

Dan Harriman 84 F150 lwb
Orange, Texas
I know this is an old topic, but I have a question. From the vacuum cannister there is a foil covered cardboard hose coming out of the end of it. Where does that go? Mine is unattached just sitting open. I wonder if that is my problem.
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Old 10-03-2008, 07:26 PM   #5
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Check the emissions label for the vacuum hose routing diagram. It will show you where they all go. It should be on the air box.
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Old 10-03-2008, 10:19 PM   #6
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Not sure what all changed, but there seemed to be few mechanical differences between the '87-'91 (Generation 8?), and the '92-'96 (Generation 9?) series.

Going further out on the limb of assumption - suggest to check that the blend door is indeed vacuum-operated - mine is still done the old-fashioned way - by cable. Pretty easy - just pop the glove-box out - have full access and view.

Now, if the air stops coming out the vents and starts coming out the floor - certainly agree with a vacuum leak somewhere, but the temperature shouldn't change - unless there's something funky going on with the recirc vacuum motor located out in the passenger side engine compartment. BTW - the vacuum line to this motor on mine failed, causing unusual air diversions from the vent to the floor.

Also, haven't dug too far into it, but I think there's two tomato cans for vacuum -
one on the passenger-side fenderwell, and the other on the driver-side, underneath
the washer fluid reservoir.

As for the foil hose thing-a-ma-jig - not sure that's coming off the vacuum system canister - suggest it may be an emission control canister of some sort??????
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Old 10-05-2008, 09:58 AM   #7
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Quote:
Originally Posted by kc5gxl View Post
I agree with you, buck8200, it is probably a vacuum problem, not a blend door problem. I have seen very few blend doors, or even distribution doors actually go bad. It is usually the controls. The give away to me is the 'thump'. I would also check the vacuum tree on the firewall, the vacuum cannister, looks like a big soup can, and all the vacuum lines. Sometimes if all is quiet with the engine running, and moving the selector switch while listening, a vacuum leak can be heard.

Good luck on the repair, and let us know what you find.

Dan Harriman 84 F150 lwb
Orange, Texas
Can you buy a new vacuum cannister? Mine corroded and I accidentally knocked a hole in it. I think it is the problem.
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Old 10-05-2008, 10:00 AM   #8
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As for the foil hose thing-a-ma-jig - not sure that's coming off the vacuum system canister - suggest it may be an emission control canister of some sort??????
Exactly what it is. Do you know how necessary that tube is?
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Old 10-05-2008, 10:54 AM   #9
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Quote:
Originally Posted by LoneWolfTrucker View Post
Can you buy a new vacuum cannister? Mine corroded and I accidentally knocked a hole in it. I think it is the problem.
I am not sure if you can buy new vac cannisters or not...at least original equipment...but surely they are out there. If all else fails, a junk yard will certainly have some. It really doesn't matter if it looks exactly the same as the original as long as it fits the location. All the vac cannister does is to hold some vacuum while the engine is accelerating or otherwise out of, or has little vacuum.

Hope that helps some,

Dan Harriman 84 F150 lwb
Orange, Texas
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Old 10-05-2008, 11:02 AM   #10
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Exactly what it is. Do you know how necessary that tube is?
I would think the foil wrapped cardboard tube comes from the charcoal cannister, and hooks into the air filter housing somewhere, to allow the fuel fumes to be burned, instead of being vented to the atmosphere.

As to whether it is necessary or not, your state smog or inspection stations rules and regs have more control over that than whether it helps the vehicle run better or worse!


Have a great day,

Dan Harriman
Orange, Texas
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Old 10-05-2008, 11:02 AM
 
 
 
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