A/c comes out of front defroster. I also found a vacuum hose lose near the front firewall and I cant find out where it goes.

Hoses should be run from motor through firewall somewhere...also check for vacuum (ball) Usually ball shaped...this ball stores vacuum to help operate vacuum accessories. Also...I've found problems with the control panel itself...partially electrical..and part vacuum...usually several hoses coming from it. I have a 96 Safari...a lot of similarities.

check small vacuum hose on rear of square inlet manifold top that goes throught firewall ( bulkhead ) is not cracked or has come off
it goes into cab near heater hoses. this is the vacuum supply hose
if you have no vacuum the heater controls default to go to windscreen. also check the black & white plastic little round one way valve for leaks & operation
also check vacuum hose that goes onto heater tap that is in right inner gaurd under brake master cylinder area for leaks and that its on the heater tap valve
if they are all ok check inside do you hear any hissing noises behind dash controls or down at front centre console area?

Check the vacuum lines in the engine compartment that go to the firewall if your A/C switches to defrost on your 1997 Cadillac Deville. Find an approx 1/4" rubber hose that goes into the firewall around the center of the firewall and trace it back to the motor and make sure it hasn't come loose. If not that, then it may have come loose at the a/c control panel. hope it can help you and good luck---------------------------------------------------------------------------------------------
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nothing. they are breather hoses

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.

vacuum hose is loose somewhere. the vacuum from the engine pulls the actuator that switches between vent, floor, and defrost. good place to start looking is near any kind of splitter or coupling in the vacuum lines. one splitter is usually just under the hood mounted on the firewall. usually on the driver or passenger side, not usually middle.

I had same problem . There is a vacuum resovoir tank located behind the left front splash shield . The vacuum line behind the battery goes to it . I removed two 5/32 screws just in front of the tire that hold the splash shield to the fender , carefully flex the shield away from the fender and take a look . I found the vacuum line had come loose , plugged it back on and everything works . Hope this helps

The AC functions of defrost, vent and floor are controlled by vacuum motors, you have a vacuum loss problem from the engine, check for a small disconnected vacuum hose under the hood from the engine to the firewall..

I'm pretty sure the door that directs the air between the defroster and front vents is vacuum actuated. Check the vacuum lines in the engine compartment that go to the firewall. Find an approx 1/4" rubber hose that goes into the firewall around the center of the firewall and trace it back to the motor and make sure it hasn't come loose.

If not that, then it may have come loose at the a/c control panel. That will be much more difficult to get at to check. You may be able to access it through the front of the dash.

Good luck.

It is a loose vacuum line, and you'll just have to trace it by hand as to where it needs to go. You might be lucky and have a vacuum line diagram under the hood, or you could buy a Haynes or Chilton's manual for the diagram. Vacuum is what controls the dampers in the air box(s), and with that line being loose you aren't getting sufficient vacuum to move them.