Ac is blowing out of the floor vents intermittently.I know I've read something on here about a vacuum operated diverter but I could'nt find it by searching.Somebody refresh my memory.Where is it and whats the usual culprit,vacuum leak?

CB

 

Mine is doing the similar thing. Mine definitely has a vacuum leak on the vacuum module ? near the passenger side firewall that has a white vacuum hose going from it through the firewall. I just have not had time to replace it lately. I THINK that this is where the vacuum is coming from that does what it needs to do but am not 100%. I just received a vacuum manual for the Bronco by Ford but havn't had time to open it up.

 

I think almost everybody has this problem. It could be caused by any of the hundreds of vacuum lines under the hood and dash. But I would start by checking all of the small colored ones that go to the AC vent system, and the vacuum canister on the passenger side of the truck.

Mine is not severe, and it seems like such a pain in the butt to go over all of those lines that I have yet to fix it.

But here is a quick fix, if you live in a part of the country like me where you only need the AC vents in summer, and only need the defrost vents in winter.

Locate the module that controls the opening/closing of the door that diverts air to either the vents or the defrost/floor. It is about midway under the dash on my 90 and can be seen if you stick your head down there. If you are not sure, start the truck and switch the AC from "vent" to "defrost." You will see it open and close. Anyway, when you have the truck running and the a/c set to blow out of the vents, use a zip tie to tie the actuator in this position. Then it will always blow out of the vents no matter how hard you hit the gas. However you won't be able to use the defrost or floor vents.

For me this is not a problem, but if you live somewhere like Florida, where I used to live, and need to switch from vent to defrost all the time, all year round, this would not really be a satisfactory band-aid. But in Colorado, it works great. I have never needed to use my defrost anytime but the dead of winter, and never need my AC vents any time except for summer. So once the cold weather hits, I just cut the zip tie. For some reason, I can run the dash vents on "heat" and never have them go off. It's only when the A/C is running.

 

BTW - when you say "inermittently," do you mean that they switch to defrost when you give it more gas? For example, if you are just cruising along, are the vents working fine; and then you go up a hill or stomp on the gas and the vents switch to defrost? That's a vacuum problem.

 

I had this problem and fixed it last week. My problem was intermittent in the sense that under the same conditions, the problem would not always happen. I bought a $20 handheld vacuum pump with a gauge (one of the more useful tools I have purchased btw) and traced the problem back to the check valve that is supposed to keep vacuum in the A/C controls when the manifold vacuum is less than enough to power the motors. The valve costs about $5 and is in the Help! section at Autozone.

Put the vacuum pump on the inlet side of the check valve and a guage on the outlet and pull about 20 inches of HG vacuum. Then release the vacuum on the inlet, and the outlet should hold it's vacuum indefinitely.
From there I would check to see if the reservoir has a leak. Pull vacuum on it and it should hold indefinitely also. If that holds, the next logical step would be to check each one of the motors to see if one is not holding vacuum.
On my truck this is easy because there is a vacuum harness located below the dash with different colored vacuum lines being connected. If you are looking at the dash, the part coming from the left is the switch side (don't worry about it for now). On the right side of the harness pull vacuum of the colored lines. Each line should hold vacuum, but the black one will take longer to reach the same level of vacuum because it has to evacuate the reservoir also (this is the vacuum source line to the switch which then distributes vacuum accordingly). If any of the lines do not hold vacuum there is either a leak in the line going to the motor or a leak in the motor itself.
As for the switch- the only position that mine will hold vacuum in is DEF. I don't know why this is yet, but I have checked one other switch and it acted exactly the same way, so I am ruling it out as a vacuum leak for me for now unless I further experience problems.

Hope this helps. If you need any more info on which colored lines go to which actuators let me know because I recently went through and found out one by one and I have it written down somewhere around here.

 

Where is this check valve located? For $5 I'd just replace it to see if it fixes the problem.

 

Find your vacuum reservoir, or, as some call it, vacuum canister. Trace the vacuum line away from the canister and soon you will come to a small plastic device that has the line from the canister running into it and one vacuum line heading into the firewall and another heading toward the engine. This is the check valve.

If your Bronco has the old, metal vacuum canister that looks like a small coffee can and there is any rust on it, suspect leaks. Mine looked fine and solid, but rust had eaten away the seam under the canister. I replaced it with a round, plastic reservoir that I bought at Ford. This took care of my vacuum problems.

I had spent much time trying to find the leak in the vacuum lines and even replaced some of the lines. The check valve was okay. I began inspecting the canister very carefully using a strong light and listeing to it using a hose and pushing on the seams as the engine was running. When I pushed on the side of teh canister, a loud hissing noise was heard. That is how I discovered the leak in the seam of the canister.

 

Thanks. One day when I'm really bored I will check this out.

I also have the problem of the cruise control not holding speed on long, gradual inclines or going into strong headwinds. It slowly drops until it drops 10 mph, and then cuts off and I have to reset it. I believe this to be vacuum related as well.

I live in Colorado, average 5,000 ft above sea level or higher. When I drove the truck to Florida last year, I didn't have the vacuum problem at sea level. The cruise held fine. I think I have a very small vacuum leak, and the performance loss at high altidude causes me to have to give it just a little more pedal, and reduces my vacuum just enough to cause slight problems. The cruise holds fine on level ground, and the vents work properly. I am going to check those canisters very well. I think that the one for the cruise is on the driver's side, behind the headlight; it's not the same as the A/C one.

 

Thanks for all the help guys.I remember when I replaced the heater core there was a door there with vacuum connections that if I remember right could direct the air to either vent.Is that right?? I plan on checking for vacuum leaks first.

Thanks,
Bill

 

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I checked all 3 of my check valves (that's all I could find) this past weekend and the were all OK. I FINALLY found my vacuum problems on my Bronco. It happened to be the white line near the passenger firewall that goes from the vacuum motor through the firewall and into a connector that feeds another motor. Instead of replacing the entire line, I cut out about 6" of bad line and put some ID line that was about the same exact OD of the bad line and then used shrink rap over the entire length of the new line and my vents finally open and close like they should.