Can't change from defrost to dash vents. I think it is a vacuum problem.

Not under the hood. The "mode" door, actuator and vacuum lines are on the heater box under your dash.

the ERG shouldn't have anything to do with what vents the AC comes out of, rather the dash switch that exists for changing from defrost to main vents to floor vents controls what vents are used.

Most likely either the vent switching mechanism is dirty and won't switch the flaps -or- most likely the vacuum that is used to turn the vent flaps is either leaking and not pulling enough vacuum. You will have to get underneath the dash near the center, to check and see if you can manually move the vent flaps. If so, then most likely it is a vacuum leak in a vacuum line to the flap mechanism.

You will need to look at the area behind the dash to see if a line was left unhooked at the control panel for the a/c defroster selector. If as you said, a line was burned, you will need to find it further back behind the dash and replace it. An unhooked line will need to be reattached to a small device that may look like a bellows. The are back there is tight but if you had work done, you hopefully still have it open from the front. Any parts store can sell you the vacuum line you will need for this fix. Good luck.

I just fixed mine. The lever that opens and closes a door that directs the air flow to the defroster was broken. To be more specific, the plastic lever the actuator attaches to was broken. The actuator and the vacuum system were operating properly. It is simple to see but hard to get to. Remove the glove box and look up and to the left for a silver vacuum controlled actuator. I was able to fabricate another lever and attach it to what was left of the OEM lever.

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.

Air will only come out of the defrost vents on the dash i assume? The defrost vent is the default position when the system looses vacuum. Under the hood look for a broken or disconnected vacuum line on or near the engine in the area of the passenger side of the firewall. You may even hear the a slight "hisss" indicating a vacuum leak. Reconnecting the line to the appropriate port will restore proper vent operation.

There is a vacuum leak under the hood. Find the vacuum line on the passenger side where it comes through the firewall and follow it to the engine. You system needs vacuum to operate and without it the default setting is on defrost for safety reasons.

if it switches function even only a few then the problem is not the vacuum source (if u had no vacuum it would default to defrost mode) the problem is the dash control head vacuum mode control switch, i don't think u can just replace the switch, u have to buy the whole climate control module.

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.