I seem to have an itermittent problem with dash / AC vent randomly defaulting to defrost vents and also 4X4 select on the Automatic hubs not functioning at times. No rime or reason on when/where. Is this a vacuum leak which I don't believe it is or more than likely a faulty vacuum pump??

Any one else experience this or know of the problem/cure?

'00 F350 Powerstroke 4X4 Dual/Crew

 

I have a 99 F250 SD 4x4 and I always have to lock my hubs for the front end to engage with the switch on the dash. The Auto position on the hubs seems like it doesn't lock or something.

 

well............. I am trying to identify and fix the problem along with my A/C vents defaulting to defrost vents. There seems to be a correlation.

 

Well I haven't had a problem with the defrost yet...actually I haven't used it...haven't really needed to. But thought maybe it would help you out some

 

There's a bulletin from Ford about Vacuum Pump Troubles right here in the TSB section up top. Here's a link for you:

https://www.ford-trucks.com/tsb/full...hp?tsb=05-17-4

 

The ESOF uses the vacuum pump to engage the hubs and also control the vent position for the A/C etc.

I had a problem with the vents and it ended up is was the vacuum pump that failed.

It is easy to check the pump to see if it is working or not, it is located above the front passenger wheel well. if it is a leak the pump will run almost constant, if it is the pump it will not run at all.

If it is working (running) than you have a vacuum leak, and the most common place is down near the the hubs. If it is not working that it is most likely the pump, but also check the fuse, but you said it was random, so most likely not the fuse.

If it is the pump do not buy it from the Ford dealer, mine wanted over $210 for it. I purchased it online from a dealer in TX for less than $130 delivered to my house.

 

Is there anything that controls the pump telling it to turn on and off? Since my problem is intermittent it appears then the pump would be running at some point in time and then either shutting off when it isn't suppose to or a vacuum line leaking?

 

It ended up being a vacuum pump failure, everything now working fine. Replaced original part#6C3Z-2A451-BA which has been upgraded several times now due to problems. Several dealers indicated they have relaced many of these due to failure. Ford should cover this part due to so many problems!

 

I have a related problem with the vacuum for the hubs. What I found was a small electric valve located on the inner fender almost directly behind the battery that seems to send vacuum to the hubs when selected on the dash. My problem is that the A/C defaulted to defrost and would not let me select Max A/C. Plus, the pump ran constantly. I removed the vacuum hose from that valve and plugged the side with the "red" hose, left all other hoses connected, and the pump stopped running within seconds. Thinking that the valve was faulty I replaced it......no joy. So currently I have the plug still in the line and everything on the dash works as advertised. I still have to get out and lock up manually. Tip......replace the vacuum hoses that run to your hubs. They are probably dry rotted.

Any Ideas?

truckandjeep

 

I've replaced the pump once and the solenoid once, and both were in the last two years. Last fall the solenoid went out again. I popped the main vacuum line, plugged it with a screw wrapped with teflon tape and switched my hubs on for the winter. I don't know if I'll replace the solenoid again or just live with what I've got. I'm not sure why Ford insists on using vacuum for either system.... seems rather old fashioned...and unreliable.

 

vacum pump stopped working and fuel milage went up........
ac went to defrost mode and 4x4 doesn't work.
cant figure out why i get better fuel milage ?????
any answers on that ????????????????

 

The pump is electric which requires the alternator to work harder however I'm not sure of how many amps it draws to make a dif, the only other connection between the pump and any related power/mechanical mechanism would be the hubs....so if you had you hubs "engaged" and now they are free that would explain??

 

i have a 2002 f250 5.4 GAS engine and i think my vacuum pump is out. my vents are only blowing out the defrost position. the other day my ac just stopped blowing. after some detective work i saw that the blower motor wasnt working, so i replaced it. now it only blows out the defrost vents. before the blower motor blew, it would blow out the defrost vents only in 4wd.(in 2wd it worked perfectly) im having a hard time finding the vacuum motor cuz im only finding them for the desiel any help guys, and thanks in advance

 

As you probably have read the vents default to defrost upon vacuum failure. You could pull the lines from the pump and check it, however more than likey a failure.

 

the tsb does not help at all