If you expect an answer it would be of great help to know what make, model, and engine size in the vehicle you are asking about. Otherwise you will not receive an answer as they are all different.
As already stated, depending on the year, make, model and engine, emission related vacuum line routing is displayed on a white sticker in the engine compartment in many vehicles.
Typically there is a sticker on the inside of the hood.
If your EGR valve is vacuum operated, simply remove the vacuum hose from the valve.
Not knowing what vehicle you have, many vehicles use a vacuum supplied by the engine to operate the different positions for the air to come out. When the vacuum is absent the system defaults to the defrost mode. I would check the vacuum supply hose starting at the engine for cracks, damage and disconnection.
The Chiltons/Haynes 72300 has the vacuum circuits divided into the emissions, Fuel and brakes sections of their manual covering each vacuum hose.
Any auto parts store such as Auto Zone, Advance Auto, etcetera should have the part you are looking for.
The most typical cause of a vacuum leak is a cracked vacuum hose. The hoses get brittle with age, and cracks are common.
You can find a detailed vacuum hose schematic for a 1984 Oldsmobile Cutlass Supreme in the car's owner's manual. You can also check with local auto stores.
If you are talking about the emission control system vacuum schematic, purchase a Haynes manual and turn to page 6-2.
It is located underneath the hood. You might have to clean it off with a rag to read it.
Try the dealer Parts Department, they have all the service manuals an what u need.
Vacuum hose diagram for 1959 chevy truck, wiper motor?
need vacuum hose diagram fast idle ac
You can get a 1996 Chevy Corvette vacuum hose schematic diagram at most Chevrolet dealerships. Your local library will have Chevrolet Corvette service manuals with the diagram.
I can' help with a diagram. I can just suggest you do them one at a time, so as to not need a schematic.
You can find a vacuum hose diagram for your 2005 VW Jetta at your local VW dealership. Most local libraries will have VW service manuals with the vacuum hose diagram.
To find a vacuum leak. the vacuum hoses should be sprayed while the engine is running. A solution of dish soap and water sprayed on a leaky vacuum hose will cause it to blow soap bubbles. Spraying both the hose and the connectors should find the vacuum leak quickly.
97 trans am vacuum schematics
There should be a vaccuum hose schematic on a sticker somewhere in the engine compartment.