I did a search and couldn't find the answer to my question so here goes. I have been having problems with the ESOF and started t/s it today. I found the vacuum hoses that go to the hubs were badly deteriorated and replaced them, went for a test drive and still defaulted to defrost. So I capped the lines coming from the wheel well to see if I need to rebuild the hubs and still the same outcome. I started doing some troubleshooting with the KOEO switching the 4x4 switch from 2wd-4wd-2wd and found that the pump is working and I am getting vacuum to the reservoir and to the climate control but the vacuum valve seems to not be working. I took off the elbow on the line that goes over the vacuum reservoir (I think this is the one that goes to the hubs) and turned the 4x4 to 4hi and the pump started and there was no vacuum at the elbow that I disconnected. Am I correct in assuming that there should be vacuum there after I switch to 4x4?

Is there supposed to be voltage to the vacuum valve plug as long as the 4x4 is engaged or is it for a short period of time? I didn't get the meter out yet until I know what it should be reading. I think there are 3 wires going to the plug. I just want to make sure that it is the valve and not wiring.

And if my problem is the vacuum valve not opening why would the climate control default to defrost if there is no vacuum leak?

 

So is there anyone out there that has a schematic for the vacuum valve? I looked on the online workshop manual and did not find any schematic's. >HERE< is the link to the manual I have. Any thoughts why the climate control is defaulting to defrost?

 

Here is a bump. Sorry I cannot help further

 

Here's a link. Even though it talks about replacing/maintenance on the needle bearings, the first part talks about the relationship between the vacuum and your a/c system.

Welcome to guzzle's 4x4 Needle Bearing Maintenance Web Page

 

I think I have a good understanding of how the system interacts with the a/c but I want to check the wiring to the valve before I just replace the valve. I will have to just probe it and find out what voltage I get and when. I was hoping someone had an idea of what to look for.

 

I'm having the same problem right now myself. I have a thread on it. Dont know about any of your questions. I did find that my vacuum is leaking off at the passengerside hub. I just replaced all the seals when I did ball joints a couple weeks ago. So I dont know what the heck is up. I am pretty sure that the pump is not suppose to run the whole time the hubs are locked. Its just suppose to build enough vacuum and cut off.

 

Update on the t/s. I probed the wires on the valve plug and found out that there is 12V to the center wire at all times the key is on. There is no voltage on the other wires which makes me believe that the computer grounds the other two wires to get the valve to open and close when 4x4 is selected. The valve is working but there is a major leak somewhere on it and there is no vacuum being built on the black hose coming from it. So I am 90% sure that a new valve will fix my problem. I am getting good vacuum to the valve but not after it. So I am getting a quote from FTEparts to see if they are any cheaper than the local stealership.

 

7C3Z9H465A is the part number, I sent you the link via my web site. I can get you a wiring or vacuum diagram if you need it. let me know.

Ed

 

Thanks Ed,
I ordered the part and hopefully this will take care of my problem. I don't see why it wouldn't. I got the link and I don't think I need the wiring or vacuum diagram as of yet. Will update everyone when I get it and install it. Thanks again for everyones help.

 

Well got the valve yesterday and installed it. This was my problem for the most part, the 4x4 is working now but have a new question. I put the truck in 4x4 and hubs locked and A/C stayed where it was set but I found that the vacuum pump will run constantly when in 4x4 while driving, if I stop it will run for a little bit and stop. Is this normal operation or do I need to replace the seal at the wheel? Could someone check to see if this is normal? I would think while the truck is moving it is loosing vacuum around one of the seals. The leak is not bad enough to make the A/C default to defrost but if this is not normal will it suck dirt/water into the bearings?

 

I beleive that vacuum is only applied for a limited time, 30-40 seconds to engage the hubs, then again for a shorter time to dissengage. I'm under the impression that other than those two events, the valve should be closed, i.e. no active vac to the the hubs. What you describe seems odd and certainly does not support what I thought I clearly understood (wouldn't be the first time I clearly missunderstood something...lol)

You might try back probing the connector when you actuate the ESOF. I beleive you will find the actuation signal "turns off" after 30-40 seconds... If so, there is something else going on causing you to loose vac pressure at the pump.

FWIW - I have a 6 mo old OME valve that just went bad on me. It leaks all the time at the diaphram (I think), but otherwise actuates/operates as expected. Basically the pump would staty on all the time. No worries though, having just installed a set of manual WARN lockers I plugged the line to the valve and all AC ctrl stuff is working now.

Perhaps road vibration while moving is opening a very small leak somewhere between the valve and the pump?? It takes very little reduction in vacuum to turn the pump on.

 

MR5X5 is correct. The system works for 30-40 seconds to create a vacuum in the hub. The factory service manual also states it could take up to that amount of time to disengage. If you are getting constant running of the motor you definitely have a leak somewhere. Start with a vacuum gauge at the hub and see if it holds, then work your way back. The service manual has a whole set of inspections to perform for the system.