I was given this 1994 Ford F250 with a 7.5 liter (460 cid), automatic transmission, from my brother. Overall, a pretty nice truck, but does have its problems. I had worked as an automotive/school bus/truck mechanic for over 20 years (1975-1996). Also, trained in the U.S. Army, to be a generator repairman. I briefly worked for 2 motion picture trailer supply companies as a generator mechanic, for close to 3 years. When I was a mechanic, I had several Chilton, and Motor, professional manuals, including one that was strictly vacuum diagrams for specific years of older trucks. But now, Chilton was bought out by Haynes (which in my opinion, is worse than Chilton), and have been told by Haynes that everything is now on cd's. I have been trying to find a complete vacuum diagram (heating system included) for my '94 Ford f250. When I do a search on the internet (using several different search engines) for a vacuum diagram, the stupid search keeps coming up with electrical diagrams. There is a vacuum controlled unit mounted above the heater core box, at the firewall, on the passenger side, which controls the movement of the door which moves the air to either the floor of the compartment, or up to the defrost vents on the dash. This unit is missing the vacuum supply line which controls it. I know it comes from the heater control unit mounted in the dash, then somewhere comes through the firewall into the engine compartment. But without have to tear apart all the wiring protective coverings, I'd like to check the vacuum diagram as to where to look. I've so far, not been able to locate where the vacuum line originates at the firewall. If I'm not able to locate the vacuum supply line, I will either have to run one from the heater control unit in the dash, through the firewall, to the control unit. But, at 60 years old, I'm not as agile as I used to be, and getting down on the floor, and reach up under the dash isn't going to be easy for me. So, I'd appreciate any assistance anyone might provide, as to either where I could get my hands on a complete vacuum diagram, or, tell me where the vacuum supply line should be at the firewall, in the engine compartment. Thank you.

 

The vacuum motor that is missing its vac line, is the vac motor under the hood near the blower motor, or is it INSIDE the passenger compartment?

 

The basic vacuum circuit should be arranged as follows:


Line from vacuum source through the firewall to the dash-mounted HVAC control.
From the control, individual lines go to each of the vacuum motors that control the doors for selecting inlet and outlet airflow.

You'll need to pull the head unit out and check the vacuum lines.

 

The unit is in the engine compartment.

 

That is the Outside Air/Recirculation door vac motor. Under the hood, look at where the vac motor is mounted. About 4-5" from the vac motor's output crank, there is a harness that comes up out of the black plastic, coming out from inside. Look about a foot forward along the harness towards the front. At that point is where the white vac plastic hardline would exit the harness, to go to the vac motor. The harness continues on a bit, with the blower motor wires, cycling pressure switch wires, and the black vac supply hardline to the inside control head.

For some reason, the white hardline crumbles. Unwrap the harness from the point I mentioned, unwrapping it towards the firewall. Unwrap it enough, and you should find the broken-off end. It may be discolored, like tannish. Bend it, and if it breaks off readily, keep moving back until you find good solid line. At that point, you can slip over some rubber vac hose of the proper diameter, and connect it up to the vac motor. When I did mine, I snipped off about a 1" length of the hardline to take to a parts store to try out to get a good hose fit.

 

Torky2, Thanx for the info. A friend of mine, also a mechanic, had said the same thing.