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OK, I'm still fairly new here and want to post this up to show how I fixed the whole "My A/C only wants to blow through my Defrosters or my A/C switches back and forth when I accelerate" problem. Mine wasn't extremely bad since I had been taping up the leaks as I found them. It was still a loosing battle. Repairing 1 leak usually caused another one shortly after. So now for the pics and story.

Here's one of the first ones. It was right at the connection point for the Control valve on the vent.

The exposed tubing becomes powdery and cracks over the years. I taped over alot of the cracks but it still wasn't good enough.

So I split the virgin taped conduit on my 92 Bronco and began pulling out the tubing. To my surprise, the tubing that inside the plastic tubing was like new. So I cut out the part that was bad back to a couple of inches beyond and used some 7/64" Gas/Vacuum tubing that I bought at my local parts store.



P.S. old model Schrade Old Timer. Real steel blades, cuts better than any razor cutter you can find if you know how to sharpen a knife, find one. You owe it to yourself.....

Anyway back to the story.

So I took my tubing and got some Heat Shrink wrap and went to work. Get shrink that will just fit over the ends and a shorter piece that is 1 size bigger.



Take 1 end of the new 7/64" tubing and press fit it over the nipple of the Control Valve for the A/C Vent. It should fit very snug and not want to fall off. Take out the screws so you can get to it easier and really slip the tubing onto it.


The reattach the unit........


Press fit the factory tubing into the new tubing. Press in as much as you can get. Here's about 1/4-1/2" in.



Now with the bigger of the Heat Shrink tubing, apply it over the connection and shrink it.

New Toy. "Honey I need this to do the job right the first time on your fathers old Bronco that he loved more than you and your Brother. It's only the right thing to do....."


Now take the other 2 even smaller heat shrinks and slide them over the original connection and shrink those over the first connection.




Resink the tubing back into the conduit and retape to seal it up. Use high temp tape for this as the cheap electrical tape won't hold up very well.



Hopefully, this will help some of the others who eventually have the same questions and need help with the repair. Pretty simple once you know what needs fixin.
 

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Discussion Starter #2
I wanted to make sure there were no leaks and that it wouldn't slip out after it warmed up in the engine compartment. I think that was the last of my vacuum leaks in the vehicle.
 

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Great post! I was just asking about this before. you probably saved me some aggrevation. Just before I went out to my truck after reading this and looked at that control valve. I started it up blasted the AC up to high and just by touching the rubber boot on the tubing where connects to the control valve I could see the valve open and close. I found the rubber boot had a crack. I just pushed it on little further and now the valve stays wide open and the ac blows like never before. I went for a drive... Perfect!
 

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Discussion Starter #4
Thanks. I decided to do it after I started to repair mine. I had intended to replace the entire tubing until I actually tore into it and found that the tubing inside the plastic was as new and pliable as the tubing under the dash. It just worked out that the tubing I'd bought was the right size to press fit to create the repair. I added the heat shrink to to it just to make sure it stayed put so I wouldn't have to deal with it anymore. I got tired of taping up the cracks only to create another.
 

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Just did this two weeks ago. didn't use the heavy tubing, just new vac tube and connectors with heat tape. Very thorough write up though. that heavier tubing looks like a great idea with the heat shrink. Good job!
 

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In case anyone here cares, I just drilled a new hole near where the vacuum lines go from the engine bay to the cab, and ran new 1/8"(?) i.d. vacuum hose to the heater goody........
 

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Discussion Starter #7
If you trace the hose back into that wire loom, you might find a length that's actually like new and still soft. Cut back to that area and use that as your splice point. Then make sure you cover it back up so it's not exposed to the direct heat of the engine bay and elements.
 

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Discussion Starter #8
Yeah, we get the "My vents only blow on defrost" posts a few times a year but I never really saw a regular fix it thread other than the one Miesk put up showing the official Ford way of doing it. That one required other adhesives and such where as this one was basically some rubber hose spliced into the existing tubing.

I think the rubber is probably more resilient to the heat and break down.
 

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Can anyone tell me more or less where that white vacuum line goes to as seen in that last pic. I'm unable to track mine down since that whole vacuum line is missing from the control valve as seen in pic #6
 

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Discussion Starter #10
It runs from the control valve under the hood, back into the cab and into the control switch behind the dash. If you remove the vent/A/C control from the dash, you should see a cluster of vacuum lines that are connected.

The loom it runs through is shown in the last photo in the Original post. It is right next to the control valve under the hood, and the fan motor.
 

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I was happily following this well-written thread (thank you!) to replace my broken white hose, and when I removed the a/c control vent, the plastic part that its attached to is totally broken off. Any idea what this part is or how I go about fixing it? This is just the next step in our process...

I have two problems:
1. Air blows out all of my vents except the defrost ones, which I need now that its winter. We also have a bunch of cold outside air coming in from the right side of the passenger floor, not the left where the floor vent is, which makes us think we have a problem with a blender door or recirc door...
2. I have no hot air out of any of my vents. Thermostat is suspect since the radiator and hoses get warm but not too hot to touch.

Much thanks in advance! I want to be able to see out my windshield this winter!
 

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Any idea what this part is or how I go about fixing it? This is just the next step in our process...

I'll respond to this one instead of the new thread, since there's pics here :)

That's a vacuum pot that controls the fresh air(max a/c) and outside vent control. When you move the associated lever at the control panel, this vacuum pot should manipulate the lever above the air box, opening or closing the door that manages the outside air introduction.

Unfortunately, this part doesn't deal with diverting to defrost.

In regards to your no-heat issue, make sure a PO didn't pull the thermostat. It's one of those things that people liked to do for reasons even they couldn't explain.
 

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I will be checking on the thermostat once I can get to it, thank you!

So I know what the metal part is, the vacuum pot, do you see the broken plastic piece that it's attached to? I don't think that was supposed to come out when I pulled the vacuum pot out... What is that called and how do I fix it?
 

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That plastic arm is part of the door that manages fresh/recycled air. It's not supposed to detach, which (unless someone comes along to correct me) you either need a whole new door or to find a way to securely refasten.

If you see the door shaft in the circular opening and the two pieces mate up properly, I would consider drilling through the top and into some of the door shaft (drill while holding it in place). Once you've done that, I'd apply some JB weld along the broken plane(not too much, so you don't weld the shaft to the surrounding plastic) and then run the screw in to secure it. Wait a day and see if you have a working fresh air door.
 

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Thanks for the info! We poked down into the hole and did not find the part that mates up to it, so either its totally gone on has fallen down and is askew somewhere. Sounds like I just need a new blender door? If anyone can find the right door for me or knows how to get to it (pretty sure I need to take the dash apart, but haven't found a good how-to on that and don't want to break anything in this cold) that would be great!

Thank you for your help! Now to find the right part and how to get it in there ;)
 

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I just followed these OP exact instructions but it did not fix my heat and AC only coming out defrost issue. Checked all vacuum lines inside the vehicle under the dash, behind the controls, all look good, however you could tell no vacuum pressure. The loss must be under the hood somewhere. All connections look good around the check valve, but I question it. Any other suggestions? Thanks.
 

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Discussion Starter #19
You may possibly have a door issue.

Search the threads for Blower Box Door or some other A/C vent search and see if you can find a few threads on checking to see if your vents are actually working. Other than that, You'll have to find any and all leaks on your vacuum lines.

Here's some to get you started.
http://www.fullsizebronco.com/forum/21-noobie-bronco-tech-questions-flame-free-zone/201462-vents-dead.html
http://www.fullsizebronco.com/forum/7-1980-96-bronco-tech/188397-low-temp-no-heat.html
 

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I just finished using this information to diagnose my AC vacuum issue and found this to be the fault. I only had to open up the wire bundle that was wrapped up and the vacuum hose was in perfect condition. I cut the end off so it was nice and pliable and reattached the end that plugs into the switch tapped it all back up and it works perfect. Thanks for all the info.
 
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