I have a newly developed vacuum leak so everything blows through my defroster vents.

Now, I understand a common leak point is the hose running to the hubs. But, if my ESOF is in 2-wheel rather than 4, how can the leak be there? I would assume those hoses are not under a vacuum so there is not way they can be the culprit.

That would mean to me, if the vacuum loss only happens in 4L or 4H the leak is in that system, but if it all the time, the leak has to be elsewhere.

Am I wrong and why?

Steve

 

Simply pinch or cap the line to the ESOF side of the container. If the condition still exists, the leak is in the HVAC side between the Container and the Head Unit. Or, perhaps the container or pump itself.

 

I've also had a leak in the solenoid for the ESOF. It's mounted on the passenger side fender between the vacuum reservoir and battery.

If it's always blowing defrost then there's a leak in the main vacuum system and if it only goes to defrost when you make a selection on your ESOF switch then it would most likely be the solenoid or downstream (as pirschwagon said).

Another thing to consider is the wear and tear on your vacuum pump. If you have a vacuum leak then your pump will continuously run...and it is not designed to. With the price of the pump you would think it would be designed to but it's not. It should run for a bit to build up vacuum when you first start the truck (if necessary) and run intermittently to maintain it. HVAC and ESOF are the only two things I know that use vacuum on our trucks. Gassers make vacuum but the diesel does not requiring a pump.

I've had various leaks (all in the ESOF). My last one took me awhile to chase so I ended up unplugging the vacuum pump so I didn't fry it. Once you've shelled out the dough for one of those, you don't want to rush out and buy another one.

 

Thanks for the input. I haven't had time to start working on it yet, but will post when I find the culprit.

 

Do you have the "colder A/C" mod over your passenger side valve cover? If so, that could be your culprit. I had mine come loose there (vacuum line) and cause everything to blow out the defrost for a minute on start up. The vacuum system was able to "catch up" after that minute and redirect to the normal vents, but as soon I turned off the truck the vacuum would leak out through that line that disconnected. Hooked the line back up and all back to normal. I think it got knocked off when I was working on my alternator wiring.

 

I haven't modded anything, but will check all connections. My pump never catches up.

Thanks,

Steve

 

I could find no leaks in my system (with extensive testing), but the vac pump ran continuously and my A/C was stuck on defrost-mode. I bought a vacuum pump from Rock Auto, installed it, and all has been well since. I can't explain... but my wife is happy with working A/C.

 

I have it fixed and the fix was simple. For whatever reason (and I can come up with nothing), the last time my truck was at the dealer's, they must have unplugged the vacuum pump because the plug was just hanging there. As soon as I plugged the pump in, it built a vacuum and everything was fine. Is there any reason to unplug it for any kind of diagnostic not directly related to the vacuum system?

Since I had the hood up, I decided it was a good time to learn the vacuum system to my truck using the layout pirschwagon posted in this thread (thanks I have printed it off for future use). I have a vacuum pump and used that on all my lines and they all are good including the ones to the wheels for ESOF.

Now here is a question. When I tried to pull a vacuum back to the solenoid, I could not do it. I can pull one with the lines detached off the solenoid to the components the vacuum feeds, but not from the component back through the solenoid. Is that correct?

My ESOF hubs still do not work and I guess it is the seal in the hub, but I don't use them often so for now that is okay (never has worked since I got the truck five years ago). I don't want to switch to manual hubs, so that will be a future project.

Thanks for all the help,

Steve

 

These statements contradict each other. If you pulled the lines from the solenoid and tested each one to the hub satisfactorily then the seals are fine.

You don't need a lot of vacuum to activate the hubs. I don't remember how long the solenoid cycles for but you only need to get above 10" to lock the hubs and above 5.8-7.3" to unlock.

If you can draw a vacuum with the pump and it holds from the line to the hub then your hubs are fine. You might have frozen/gunked up locking hubs (separate from the wheel hubs) and you can try this:

Welcome to guzzle's 4x4 Autolock Hub Lubrication Maintenance Web Page

I have used this successfully to keep my OEM hubs working (280K miles) until I went with manual hubs.

I still don't know if you are in defrost all the time or just for a couple of minutes when you try to engage/dis-engage 4wd. pirschwagon has a good half-splitting idea. By removing a few vacuum connections you can narrow down the problem. A few items that are harder to diagnose are cracked vacuum lines, bad vacuum pump, and bad solenoid.

I will say that if you have any caps on vacuum lines that you check them first. The environment under the hood is not the best for rubber. You might only need a $2 fix and a run to the auto parts store.

I've read of the pump itself being the actual leak and I had a leaking solenoid. I disconnected all the lines from the pump, reservoir, and solenoid and tested each one. If you don't have any rubber vacuum line caps it can make it difficult. I didn't have at the time and everything tested satisfactory so I figured the solenoid was the problem. Replaced it and problem fixed. If I were doing it today I would have a bunch of vacuum caps to test everything with a vacuum pump. I rolled the dice and came up lucky because an OEM solenoid is not pocket change:

Pulse Vacuum Hub Solenoid Valve

You can buy an off-brand for about 1/3 the price.

 

Please see my last post. I do not have anything approaching 10" HG and the hubs are locking and unlocking find.

Thanks,


Steve

 

My bad, I somehow glazed over the solenoid question. I don't know what to expect in it's ground state. My last foray into vacuum issues was the solenoid. I tested everything else and was able to draw >10" vacuum on each line to the hub (25"). After eliminating everything else I took the leap of faith and replaced my solenoid and it turned out to be the culprit. Since all it does is either allow vacuum through to the hubs or not I would think that it should hold vacuum if you put the tester on the pump side connection.

As for the hubs, I apologize if I misunderstood. It sounded like you were able to draw a vacuum to the hubs with your tester but the hubs were not locking. That would indicate that the seals were in good shape (can draw a vacuum) but that the auto-locking hub was not activating (indicating they were frozen or damaged).

 

Hey Brian, not a problem. I realized you missed the "I fixed it part". You are right about my contradiction. I was thinking frozen hub, but sure didn't type it.

I am still trying to figure out how I could drop it off at the dealer's to get the alignment checked and get it home with plug to the pump disconnected. If I had two cents worth of brains I should have immediately noticed I could not hear it on start up for few seconds, but that is what the learning curve is about.

Steve

 

Maybe they were giving you the "free 150 point inspection" and "accidentally" bumped the plug.