HI all, I just recently purchased a 1999 Ford F250 SD 4X4 XLT with the 5.4L. The truck needs a bit of work but overall its in pretty good shape. My plan is to restore it, use it for a few years and then give it to my son for his 16th Birthday.

Mechanically the truck is in pretty decent shape. However, it is not without its issues. The first one being the HVAC system. I have a 2 part problem.

1. The AC works great but there is no heat. I already purchased a blend door actuator as I figure I cannot get lucky enough for it to be a fuse. regardless I have a good starting point on that problem

2. The air will only blow out the front vents. switching it to the floor or the defroster setting does nothing. Is this also blend door related or vacuum related?

Tomorrow I plan on checking the actuator but I am at a loss for the vents only blowing out straight.

Any additional help is appreciated. Thanks Frank

 

OK so after troubleshooting I have verified that the fuse is good the blend door actuator is moving, and as far as I can tell the blend door is moving (using a 1/4in extension)

So with that said, the symptoms are the AC, MAX AC, and OFF positions work the AC blows cold, but only out of the forward facing vents.

-turning it from cold to hot does nothing air remains cool or ambient (depending if the aC was on or not)
-adjusting it to any other position such as defrost or floor does nothing

Suggestions?

Thanks

 

so nobody has any insight?

 

Start with the FAQs (above).

 

Yes I saw the FAQ's the closest one if any to mine is this one :

"Problem: Air flow has defaulted to the defrost vents (either all the time or under acceleration).
Solution: The system is designed to default to the defroster in the event airflow control is lost. Intake manifold vacuum is supplied to the control head, whether manual or automatic (electronic) to operate the vacuum motors.. A very common failure is a split, cracked, or otherwise leaking vacuum line located between the battery and firewall. Other causes include a leaking vacuum reservoir (inside the right front fender), faulty check-valve inside the dash, or other vacuum leak in the system."


The problem is that mine has not defaulted to the defrost vents, it has defaulted to the front vents. Also I have no heat only A/C and only out of the front vents. No other position works, hot and cold mix **** doesn't work, the position A/C, MAX A/C and off work.

I tested the blend door and actuator both appear to be good

is the HVAC also vacuum actuated on the 5.4L or only the diesel?

 

Also not this:


Symptom: Can’t change temperature. Easily confused with a stuck/broken blend door.
Problem: Stripped Temperature ****
Solution: Replace **** with a new one from the dealer.

As the **** makes the actuator move

 

Good. Now that you've covered the common stuff and confirmed those are not issues, we can dig deeper.

Issue 1 (No heat) : Did you verify that there is hot coolant circulating through the heater core? If that isn't happening, you'll never have heat. Some vehicles have ended up with a vacuum-controlled valve in the heater hose line under the hood that's supposed to shut off coolant flow when in MAX AC. Check if present, if so, check its operation. Check coolant level. Check for a clogged heater core. Check water pump operation.

Issue 2 (Stuck on panel/vent): Inlet and outlet airflow are controlled by a set of vacuum motors that, via bell crank linkages, move doors inside the HVAC plenum.

You have to verify several things:

A: That the mode select switch is properly directing vacuum to the correct vacuum motor in each necessary position.

B: That the vacuum motors are receiving that vacuum signal (unhooked hose, for example).

C: That the appropriate vacuum motor retracts and extends in response to the presence or absence of vacuum at its control port.

D: That the bell crank and linkage is connected to the door's lever and that the lever actually moves the door inside the plenum (ie, not jammed or broken).

I'll see if I can dig up some diagrams later this morning.

 

In the attached file, pay particular attention to the operation of items #17 and #1. Use the vacuum application chart and connector table to determine when you should and shouldn't have vacuum at each hose/motor port.

The motor for the floor/panel door is behind the glove box and to the left.

The motor for the panel/defrost door is up above the gas pedal.

 

good deal, I plan on driving it and troubleshooting tomorrow. As far as I know the heater core hoses are both hot. when I checked the truck was barely warm though so a more thorough check will be done tomorrow when i drive it to work. that is a great diagram and is exactly what I was looking for.

Is it possible that the there is a leak or break in the vacuum line somewhere which is prohibiting the selector to switch between the A/C and the regular panel vent? (if that makes sense) which would possible cause both symptoms? It doesn't look like it would as it looks as if the air flow is through the evaporator in either scenario though(according to the diagram). meaning that the only way i wouldn't get heat is the blend door, heater core, actuator, or low coolant.

 

unless....it has that valve to divert coolant for the A/C that you mentioned, then it would make sense as a loss of vacuum would ultimately divert coolant from the core. Also, I know that a newish motor was put in the truck before I bought it...maybe they forgot to hook up a vacuum line.

 

No. The valve is designed to be open unless there is vacuum applied to it.

No. See the diagrams I provided to see how it works. Once you understand how it is supposed to work, you can easily figure out what's not proper.

 

Ok so far I have found 2 severed vacuum lines at what i believe was the hub locking solenoid for the 4wd. (Box to the left of the vacuum canister) the hard lines were cracked so I spliced them in and also replaced a dry rotted segment on the top of the canister. I now have the floor vents working ...still no heat or defrost.

For the heat I checked the coolant, it was at the appropriate level

felt the heater hoses neither were too hot but they were both the same temp.

 

If the engine is fully warmed up, those lines should be hotter than 180F.

Are you saying you can now switch between panel and floor? If you have NO vacuum going to the system it's supposed to all come out the defrost vents. If it doesn't, something must be mechanically jammed.

 

I checked the hoses once I got to work after about 45min to an hr. they were warm but not hot.

After repairing the two vacuum lines that run to the 4wd hub locking solenoid (thing mounted on the passenger side inner fender to the left of the vacuum canister I was able to get the panel and floor vents to work however, the defrost setting still doesn't work and the heat still doesn't work. the two broken lines were black and red in color I believe the black was a main line.

on a side note my 4wd ESOF switch is not engaging 4wd either I know the 4wd light not coming on is either the transfer case motor or electrical but thats another problem I just discovered that i will fix once i figure this one out.

this truck is full of gremlins