I have a 2000 excursion v-10 limited. Yesterday coming home from the cape while towing a trailer I had the AC on full blast. I noticed that when I got on the gas, my AC would eh...stop blowing out of the dash pannel vents and blow out of the defroster. Got home un hooked the trailer and played with vac lines took the dash apart and checked all connections. I did not find a leak or hear one. Took it for a ride and it would only do it when I got on the gas to pass or while getting on the highway and coming up to speed. Hooked up the trailer today, and it did it while getting on the highway, and every time i got on the gas and especially when it down shifted to climb hills. Anyone run into this? I posted in the excursion forum, and I got a million messages about the vac pump, but eh, its a gasser and it does not have a vac pump. Diesles do. Any advice would be great thanks

Dave

 

If you have ESOF (regardless of engine) you do have a vacuum pump. The vacuum is used to lock in the hubs. One classic sign that you have a leak somewhere in this system is that your AC will blow out the defrost vents.

So first question is do you have 4x4 and is it ESOF?

 

It's happening during times of low engine vacuum so I would look at the check valve in the vacuum line going from the engine to the vacuum canister on the passenger side in fender under the hood. The canister runs all the vacuum equipment when the motor is under heavy load. But if the check valve is not working the vacuum will not hold in the canister and the A/C controls will fail to work.

Denny

 

If it's a gasser, he does NOT have a vacuum pump.

To the original poster, if you have the 4x4 switch on the dash, pull the vacuum lines from the vacuum solenoid, just behind the vacuum reservoir behind the battery. Plug the (I think) red line, whichever has vacuum all the time. The vacuum solenoid might be leaking.

If it still does it, check for vacuum leaks, like a cracked reservoir, broken vacuum line, etc.

 

Well I was calling the ESOF vacuum solenoid/reservoir a pump but that is not the right word.

EDIT: The red line is the vacuum line. You can confirm it by looking on the reservoir it will have "VAC" for that line.

 

Gentilemen, I would love to be able to find this check valve. ok, well I think I know what its NOT. I by passed the 4x4 vac lines completely, and had the same issue. NOt the 4x4 apparently. THen, I bypassed the entire vac canister, and everything else and connected the interior cabin vac line right to the vac feed line comin of the intake manifold. Took it for a test drive. happend again. used a vac pump to suck down the vac at the the selector switch while the line was disconected from under the hood and plugged. It held vac. Plugged all the vac lines back into the switch, and sucked it down from the other side. It held. Ok no leak inside the cabin. Then the cansister itself, held vac. OYE. I did learn that the RED lines, do not hold vac, because they all T into the intake manifold, dur. Only thing I can think of is that I am not losing vac through a leak. I am failing to maintain vac. when stepping on the gas, you lose vac, common knowledge. I am wondering if there is a check valve that prevents the vac from back flushing (in a way) when you open the throttle gate..... But ill be damned if I can find it. Spent 12 hours today working on this with 3 of my mechanic friends. I do have a V-10 GAS engine. its a 2000. Where oh where is my check valve?? Id love to find the bugger and test it. A photo would be WONDERFUL. If ya got a camera phone, email it to me or send it to me via text...BAM7722@aol.com will hit my blackberry.

 

I looked today and it has to be the rubber fitting that goes into the vacuum tank. It's the same one that has the inlet hose and the outlet hose attached to it. I did not take mine off because I did not want to brake it. When I disconnected the red line (inlet) I lost no vacuum but when I disconnected the outlet line I lost vacuum. So it's in the rubber fitting or in the tank but I bet it's the fitting. My truck has been setting for 2 days and it still had vacuum in the tank.

Denny

 

Denny, Can you please, OH PLEASE, OH PLEASE OH PLEASE send me a photo of this fitting? and your tank so I can see if it is the same tank I have? YOU could save me 91.10 an hour on tuesday..If yours is the same as mine, I can swamp out the tank while at work on tuesday, out of one of the many 99 v-10s we have on the lot and test it out, and if thats my issue, yikkiddy split ill buy a tank and thank you for months to come. I am afraid last time I took it into the stealership I think the tech sabotaged me (suddenly I was missing a copper crush washer on a rear caliper and fluid was suddenly leaking all over the place, suddenly my rear diff was leaking and bolts were loose...4 of them and now this, and I havent driven the truck 500 miles, the wife has it most of the time) So I would LOVE to see what it looks like. The red hose comes off your intake manifold, and goes into like a double plug that plugs into the vac tank. The black hose then leads to other black hoses that run everything. SO I am assuming you split the red hose between the tank and manifold at one of the connections and did not lose vac in the tank? THEN you disconnected the black hose from a fitting and then LOST vac? PLEASE send me a photo, Bam7722@aol.com. I am wondering if there is a check valve INSIDE the tank... that has gone south..... ALSO, please explain how you know there is still vac in the tank...do you have a gauge?

 

I will send you a email with a easy fix.

Denny

 

The easy fix is to install a older style vacuum check valve in the tank inlet line just like all the old Fords used cars and trucks.

Denny

 

I have this exact issue with my 2000 F350 4x4 CC SB V10 with 115k. While pulling my 28ft TT the A/C intermittently would blow through the defroster when pulling any hill or when I turned into a stiff headwind. Could you post a picture or provide more details on your “easy fix” for my vacuum leak.

 

I don't have a photo of it because mine still works fine. All you have to do is replace the rubber manifold on the bottom of the vacuum tank or install a check valve in the line going to the motor.

Denny

 

Do I need to remove the vacuum tank to find the rubber check valve? I pulled the main vacuum line that comes of the passenger side of the throttle body and didn’t find any check valve. Also pulled the red vacuum line that run to the vacuum tank and didn’t find any check valves. Could you provide a little more detail were to find the rubber check valve. Thanks

 

I don't want to pull my apart (if it's not broke don't fix it) but its ether in the rubber manifold or in the tank itself.

Denny

 

UPDATE…LOSS of VACUUM. As described in the above thread my A/C would intermittently begin blowing through the defroster during towing. It would only happen when pulling a hill or during a strong headwind. It ended up being a device that is no longer used…the auto hub vacuum solenoid. My V10 has manual WARN hubs so the vacuum solenoid isn’t used but still hooked up. The solenoid must have had a very small leak that would only become a problem when the engine was working hard during towing up a hill. FIX…disconnect the red vacuum hose at the tee going to the vacuum solenoid and cap the tee. I didn’t remove the solenoid or vacuum hoses to the hubs to keep dirt out.