Hi All,

Have read through the forums but can't seem to find the exact answer, maybe I am not reading the search correctly, but my truck is fairly unique in setup.

2002, F250, 5.4, ZF6, 140k.

My heat only blows through the defroster. I was looking for my vacuum pump, but can't seem to find it. I find plenty of diesel threads where they show it, but mine isn't in the same location. I can actuate the diverter by hand and it will make the heat stop at the defroster and come out at your feet.

I have attached images of my rig.

Anyone have any suggestions on where to look for the vacuum pump? Any key spots to look for failed vacuum lines?

Thanks,
Rick
What is this?


This is where most threads say the vacuum pump should be.



This switches from defrost to floor when operated manually.

 

You don't have a vacuum pump as a gas engine creates it own vacuum. The most common place for a leak is the vacuum lines for the auto hubs then the pcv elbow.

 

I too would start with looking at the esof lines.

 

One simple way to see if the defrost door/damper is moving to defrost mode is to have an assistant change the setting while the fan is in low (1) speed. Stick your ear close to the heater box under the dash and have the assistant operate the dash control from vents to defrost, then back again. You should hear the vacuum motors moving the dampers/doors inside the heater box. If not, you either have a big vacuum leak somewhere (as mentioned), your vacuum motor that runs that damper is bad, the damper has broken off inside the box (plastic gets old and brittle), or the damper is stuck from leaves or other gunk that has made its way inside the heater box.

 

Yeah, you have the 5.4L vacuum pump.
As the other said, the most common vacuum leaks will be on the rubber lines going from the frame to the hubs for the ESOF. There have also been some failures on the vacuum switches that activate those hubs, it's mounted on the pass fender next to the vacuum canister (your second pic, where the PSD vac pumps go). Put fresh new rubber hoses on first, then if still no joy check out the switch/solenoid.
The vacuum solenoid switch is shown at the far left here, it has the black and red small vacuum lines plugged into it and the electrical plug (red/grey?/black wires, in the very lower left corner of pic) is unplugged.

 

Dang...doh! I so forget about the engine vacuum on modern vehicles! I will take a look where the hubs are, but I do not have auto hubs nor do I have a switch on the dash for them. I do remember there being a plug in the vicinity when I did my ball joint, but didn't take note if there was a vacuum line coming down.

Will check out elbow.

Thanks.

 

I did have my spouse actuate the setting while the fan was on. There was no change, nor any noise coming from under the dash. I can manually actuate the damper in my pic to change air flow from the dash to floor. So, at least I assume that one isn't bad.

Shouldn't a significant vacuum leak affect my idle and performance?

 

Only if it's significant enough.... This isn't.

This truck is a 2WD, obviously it doesn't have the hublock system. Look at the 2nd photo, see any PVH solenoid?


Find the small vacuum line that goes through the firewall. Somewhere along the line, it has a leak. Locations near the battery usually fail first. Defrost-only almost always indicates that the control head has lost its vacuum supply.



.

 

Thanks and Happy Thanksgiving!

This truck is a 4WD truck.

Honestly, I think the original owner ordered this to his specs because of some other things in the truck.

But, I will start looking for the vacuum line going through the firewall. Can I see where it goes to the control head to trace back? I would assume it's either a black or white line, correct.

 

If it's 4WD, it must be the manual version....

IIRC, the supply line is black, but, since it's the only line that goes through the firewall, it's not tough to find. It probably is one of the lines visible in the 2nd photo you posted.

 

It is. I think it's a custom ordered truck.

5.4L, ZF6 - 6 speed manual, Ford manual locking hubs, 5.13 gears - front and rear, Locker in the rear, rubber matted floor. Really hard to find the 5.4/manual combo.

It doesn't have any of the auto stuff for 4wd on the dash.

I will look...kinda dark and scary up against the firewall, LOL, but I will take a look. Is there any way to purchase the hard vacuum line to replace or would soft vacuum line be the way to go?

 

It would be a good idea to find the actual leak first...

If it's a cracked section of the hard line, use the rubber line to splice. It might be a barbed fitting, reservoir or whatever.

 

10-4. Thanks.

 

Ok, solicited another helper...

So, it's not just defrost only. If I use the left hand side of the ****, vents and AC indicators, I can get air blowing out of them.

Its only when I put the **** on the right hand side, feet, defrost, etc. does air only blow through the defroster.

Would this narrow down where I look?

Still having no luck with finding a vacuum leak.

Thanks,
Rick

 

Yes.

That would suggest that either the vacuum portion of the MODE switch has failed or that one of the vacuum lines coming off that MODE switch or its vacuum motor has failed.

See the attachment. Open it and print it out, it will tell you which colored line coming off the back of the switch (vacuum ports) performs which function is each MODE switch position.

I'd focus on the yellow and blue lines that control the Panel/Floor door.