Vacuum leak in dash- 97 areostar..

The vacuum hose on the power brake booster (right behind the master cylinder), (where you put the brake fluid) has probably popped off or cracked. If so you will hear a hissing noise & have a loss of power brakes. Either reinstall the hose if possible or replace it if it is damaged. Good Luck Frank M

Check vacuum lines.

There is no special vacuum hose, you have to check all vacuum hoses to determine this. You can start at the brake booster, while it is running. you should be able to hear a hissing sound, but not always. ( check all vacuum hoses under hood) to find leak. Is the check engine light on, If so check the gas cap to make sure its sealing properly. Good-Day!

a lot of the air vents are controlled by vacumn, some auto stores sell cheap stethescopes to help isolate the leak, before you pull the whole dash apart. change the air vent settings , may help isolate it as well

may just be a vacuum leak. best way to find out is start the car and pop the hood, you may hear a hissing sound, this would be a leaking vacuum hose or fitting. If you do not hear hissing, start with the top of the valve cover. There should be a rubber hose that goes to the brake booster, that is a major vacuum hose, start there and trace every vacuum line you see to the end....vacuum lines are mostly small hard plastic hoses, with cheap little rubber fittings, a lot of times these fittings dry rot and leak, causing the heat not to blow, cruise control not to work, bad oil pressure....you get the point, vacuum leaks are a PITA! but very important....my jeep did the same thing. All the sudden it stopped working all together. A vacuum hose had completely come apart. I spliced it together and it works like a dream....

good luck, hope this helps....

More that likely the vacuum supply hose to your heat/ ac controls is leaking or, one of the vacuum motors is unhooked or ruptured. Use a small piece of hose, if you have any, start the engine, then stick one end of the hose up to your ear and search around under the dash with the other end. Keep moving the hose until you isolate the spot where the noise is loudest.(cheap stethoscope). Use a mirror if you cannot physically see the area. That is where you will find your leak. TJ

Well, there is a vacuum canister under the hood that stores vacuum for the heater. Yes, this could be the problem, or it could also be something electrical. By the sounds of your problem i would lean towards a vacuum problem. The vacuum canister will black in color and usually round, it will be on the passenger side, usually by the heater box. there will 2 vacuum hoses on it. Are you hearing any hisses coming from the dash area, or under the hood? That is another sign you have a vacuum leak as well. Hope tihs helps you out....

check for vacuum leaks. inspect vacuum lines in engine compartment going ito fire wall just under heater hoses. also listen for vacuum leaks behind dash board. it is normal to hear a slight hissing when the mode door selector is moved into different positions for a few seconds.

this is caused by a defective leaking vacuum (that is the hiss) power brake booster diaphragm, replace the power brake booster.Use the link below for general instructions on replacing your booster, it is a diff car but the same type of part is on your car.
http://neptune.spacebears.com/cars/stories/booster.html

U have either lost the vacuum to the mode selector switch (in the dash control) or the vacuum mode selector switch is leaking in the ac/heater control in the dash, u can usually hear a hiss if it is leaking. the vacuum source is the engine, a small hose runs through the firewall on the passenger side to the switch from the eng vacuum source.