I've scoured the forum and found several threads, but none seem to apply to my situation.

03 F-250 6.0L 4X4 w/ESOF and manual heater function selector switch.

I don't use 4WD often and it started blowing only defrost, one snowy evening, when I selected 4HI. This lead me to believe that it's an ESOF issue, but she blows just defrost when 2WD is selected. When I select 4HI the 4X4 operates as it should. I checked the vacuum motor and it runs. When I remove the hose there is suction. The function selector switch does work (turns off when OFF selected).

While it appears this isn't ESOF related, I can't get past the irony that she started blowing only defrost the same day I used 4X4.

Any ideas???


Thanks,
RB

 

Have you tried temporarily capping the line that goes to the ESOF?

Best bet is to start broad... and narrow down where your leak could be.

Before you do much else - check under the passenger side dash for some vac lines (a bundle of 3 or 4 with a connector in the middle) and make sure that the connection is snug. My new puppy was napping on the floor... and while he was rolling around on his back getting comfy, managed to unplug the connector on the vac lines with his feet. It's a long shot - but it only takes 2 sec to check... and it's free. It looks like the lines could be disconnected by someone with big work boots or shoving stuff under the dash because the weather was too crappy to put it in the bed.

It's a lot easier if you have a Mighty Vac - just bought one to track down my own leak, but it works great for bleeding brakes and a few other things as well. The Mighty also comes with extra tubing, T's and plugs of various sizes to help make life easier. You could probably pick up the plugs from an auto parts store for a few bucks. Also - being able to read the pressure on the Mighty's gauge means you can see if you're losing presser, how quickly you're losing it, etc etc... which will tell you a lot more about your problem.

Without the Mighty... (much easier with the Mighty) start capping off lines one at a time to narrow down where the leak is.

First cap the pump to see if it holds pressure.

Then reconnect the pup to the reservoir tank... and cap the tank instead... see if it holds pressure. If both of these hold pressure...

Disconnect the line to the ESOF and cap it. (Make sure to cap the side leading from the pump... I watched a friend cap the wrong end...) If the A/C vent starts working correctly... you know the problem is somewhere on the ESOF side of the system.

> If this is the problem, reconnect the ESOF and start tracing the lines towards the hub, capping off a connection at a time until you find the leak. (You might do a visual inspection of the lines first - in case the problem is obvious.)

If the problem are the hubs - there are several excellent threads on here that go into more detail on rebuilding or replacing the hubs.

> If the ESOF is not the problem, then you'll want to start tracing the lines back to the A/C instead, and follow the same process of elimination.

Keep in mind - it'll take longer without the mighty vac - because you'll have to wait for the pump to build pressure each time - and see if it holds for any length of time. I personally am not that patient - but you may find a friend locally who can loan you the Mighty Vac as well.

If you do have the Mighty Vac (or something similar) - first use it to test the motor and reservoir. Instead of pumping the handle for forever... let the electric pump do it's job, wait for it to click off... and watch the gauge. (I forget what the peak pressure is supposed to be - hopefully someone will chime in.) Note the pressure though, and make sure that it can hold pressure for 5 min or so without dropping more than a few psi. Once you know they're in good order, disconnect the line to the pump and reservoir and cap it so that you're not having to pressurize the whole reservoir as you check other connections. (or connect the Mighty Vac on the end of a connection that would otherwise have lead to the pump.)

Seems like common sense once it's been mentioned... but you'd be surprised how easy it is to watch a friend screw up. :-)

At any rate... just follow the same process of elimination. Start at the Pump and work your way back. Any time there's a T... test one side... then the other... essentially eliminating 1/2 of the possible leaks at a time until you narrow it down.


If anyone knows of a faster approach, let me know - because I'm about to have to track down a new leak of my own - I have a pinhole somewhere. It's not bad - but I don't want to wear out another vac pump because I didn't realize I had a problem... and it ran until it cooked.

Good luck - let us know how it works out. If you're ever in the LA area, you're welcome to come by and use my Mighty Vac.

 

A standard (and potential dangerous) way is to use a propane torch to release a small amount of propane near suspected leaks and monitor engine RPM.

You need a vac gauge.. can't just judge by suction.

 

On a gasser that might work - the Diesels don't create enough continuous vac, so they run an external electric pump. (Burnt mine up recently because I didn't realize this... I let a leak go until I had time to fix it - and suspect that the pump running continuously because of the leak is probably what cooked it. The sad part is that it was just a line under the dash that the puppy disconnected.)

Even without a vac gauge, you could cap the ESOF to see if the A/C vent works. (You could essentially leave the ESOF capped until you had time to fix it, and not have to live with the permanent Defrost.)

Edit: That goes back to... this is just a quick and dirty fix. I wouldn't want to do more than that without the gauge either.

 

Rob, right.. I just noticed he is a 6.0..

Where was your vac leak under dash? I may have the same problem.

Can you post a pic?


How did you conclude it is a vac leak?

Did the brake warning light come on?

 

It is worth mentioning that what the OP describes is how the vacuum locking hubs work. A vacuum pulse locks the hubs going into 4WD, and another vacuum pulse unlocks the hubs when going back to 2WD. This explains his heater going to defrost in both of those situations.

It seems to be common for the vacuum solenoid itself to fail and leak when it's activated. But as TR8 said, the best way to find the leak is by systematically testing each line and component from the pump out with a vacuum pump and gauge.

 

Bring to a dealer or certified mechanic. Have them run a smoke test on the system. It could be as small as a pen hole leak somewhere.

 

Gents:

Thanks for the guidance. I finally got my Mityvac (I had to go get it. Apparently FedEx doesn’t deliver in N TX when it’s snowing). This is a great tool. Here’s a recap of the situation:

1) Heater Selection Function Switch does work.
2) Heat/AC only comes from windshield defroster vents (vent or floor not available).
3) ESOF does work.

My truck does not have lines beneath the dash on the passenger side. There is a metal panel there and the lines are behind the glove box. So I ruled this possibility out. I know the vacuum pump operates because the ESOF is working. So I began checking random lines. When I plugged (Mityvac came with numerous sized plugs & adapters) the RED line going to the ESOF Vac Solenoid the vacuum motor stopped running. I also had airflow from the vents and floor. I replaced the solenoid (part # 7C3Z-9H465-A) and the problem was solved. This part is located just forward of the vacuum motor. It has one electric connection and two hoses connect to it (black on the top, red on the bottom). I’ve attached a pic of the bad part.

https://docs.google.com/leaf?id=0B9D...thkey=CMO3t6cN


RB