Originalplastic vacuumlines availiable for 1990FordF150 302

the service manuals are by FORD, F150 , what size engine is this i6? 300cu? 4.9L sure.

for the whole car,
brake booster.
HVAC vast usage.
EGR
MAP sensor
distributor Vacuum advance
for calif engine or federal, they are not the same.
open hood and look up and under see the vacuum map there.
A/T transmission with vacuum modulator.
EVAP valves vacuum.
most 91 cars USA had that. for SMOG vacuum only.

the book is here
I pay ,you pay?
login and pay , read on all smog and all vacuum devices

https://eautorepair.net/app/CustomerInfo.asp?VID=&Count=Y

Question edited for clarity.
Question moved to sub category.

Check out the link. Also click the images tab.

https://www.google.com/search?q=2003+ford+f1-50+4x4+4.6+vacuum+line+schematics

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Dustin, Sound like vacuum loss to position switch. Defrost is the default position when vacuum is lost in vent control system. Check any and all vacuum lines and connections under hood first, especially any that run through firewall. Check the attached links,instruction and guides, Good luck
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That line breaks every where. Run a new line. drill a hole thru the firewall. Find the vacuum ball and hook it to it. Tape the line well thru the firewall to prevent rubbing a hole in it. Your best and fastest/cheapest choice. This line runs (in) the wiring harness....

Without more detail it is hard to say which diagram you need but if you copy and paste this into google.com's search field then select the word images directly underneath where you pasted it, you will see many options.

Copy and paste this;

2004 Ford F150 Ford vacuum diagrams

Or, I have added a link here that has a view of the top of the motor with vacuum lines marked.

vacuum lines on intake manifold Ford F150 Forum Community of Ford Truck...

The front hubs are activated with vacuum. You have a vacuum leak or bad chech valve in the line. Check the lines that are near the firewall and see if they are ok.

I am really sorry but we have no vacuum line diagrams for this truck.

in the vacuum line or shift motor. blow out lines and remove vacuum motor and drain.

check vacc line from engine into fire wall. behind batt is where they normally crack and leak. possible from a leaking batt at one time. check black supply vacc line right behind battery

If the vacuum lines are deteriorated and cracked, they will make the engine run rough, uneven, and hesitant. All you have to do is take the lines off one at a time (so you don't mix them up) and change them out with new lines.