Vacuum line under dash - 1985 Mercury Grand Marquis

Vacuum supply starts on the drivers side of the engine. There is a vacuum line going into the brake vacuum assist from the manifold. branching off of that line is a double line that snakes under the intake manifold, behind the valve cover, along side the valve cover on the passenger side headed to the front of the engine. Then it curves to the right side of the engine. One set of hoses from this line goes to a valve control (red and green i think). The other line goes to the vacuum storage ball, it should be black. The vacuum circuit continues out of the ball in another black line that snakes into the firewall. It goes under the heater core black box and disappears under it. Now go into the passenger compartment and drop the glovebox. look to the back right you will see a black and a white vacuum line coming out of the firewall. The black line is your vacuum supply from the engine. It goes up to a little rubber manifold. disconnect the lines coming from the dash switch and check for vacuum on the manifold where the black line is going in. The white line controls the cabin air intake under the glovebox and the thermostat shutoff under the hood. It should only have vacuum when the switch is in a certian position, AC probly. The other three lines coming off the rubber manifold snake behind the dash vent door assemble and come out near the gas peddle. The red one controls the dash vent. apply vacuum to the red hose and see if the vents go to the center dash position/AC. The yellow and blue? ones control the floor vent control near the gas peddle. yellow gives you half floor and half defrost. blue gives you all floor. you can use a small vacuum line to connect the black vacuum supply to each individual line on the manifold and check the function of each vacuum control assembly individually. I hope this helps. On my truck each control unit works fine when i apply vacuum to them individually but when I hook the dash switch up to the rubber manifold it goes to defrost. I tried changing the dash switch and the lines running from the switch to the rubber manifold and the vacuum ball under the hood, nothing works. I suspect I may have leak i just haven't found yet. next step is to get a vacuum gage and start checking the amount of vacuum i am getting at each vacuum line. I'm sure it is supposed to be getting a specific amount of vacuum and will not work if the vacuum drops below a certian level due to a leak in a line somewhere? God bless.

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???

It's most likely a vacuum line, look under your hood (close to the cowl panel) for a disconnected, cracked or broken vacuum line.

In some rear cases, it could be the vacuum switch (in dash). Or vacuum diaphragm (under dash).

Hope this helps you ???