The box can fail but it is only there to "store" vacuum so you don't lose the CC & HVAC air control when the engine has low vacuum like pulling up a long hill at full throttle. More often the hose falls off at the inlet. If the CC is not working & the air only comes out the defrost vents on your HVAC then there is a vacuum leak either in the hard line or the hose connection at the intake manifold or the T for the CC line.
Ok, 2 things. 1st go to the T near the manifold where the vacuum Ts off to the CC. Disconnect the line from the T that goes over to the HVAC & reservoir (box) & plug that off at the T opening. Now see if the CC works. If yes, you know the CC works & the vacuum leak is further down the line. 2nd access the back of the HVAC control panel & make sure the bundle of vacuum hoses are properly connected to the back of the switch & I think there may be another junction connector further away from the switch. The black hose is the primary vacuum hose from the T above the battery so concentrate on that one. If they look good disconnect them from the switch & check for vacuum at the black hose with the engine idling. If no vacuum there start rechecking the line back from there toward the intake manifold. If the hard line cracks it will leak & can be hard to find. You can further test that by running some vacuum hose from the CC T to the T above the battery (that is where they often crack from the engine heat) & also to the reservoir if needed. I know you say you have replaced the hoses so you may have already done this but be sure to check the line/hoses in the cab. You can also plug off the hose to the reservoir to check that but with the engine idling there should be enough vacuum to work the CC unless it has a massive leak.
Just to make sure the hose from the manifold to the CC T & the CC line are OK. Might want to plug off the CC side of that T as an alternative. I don't have CC & am not familiar with it enough to know if it might have an internal vacuum leak.
Well I just got done going over the lines again. I eliminated the CC and now I can see the arms underneath the dash moving as I switch to different modes on the heat/AC controls. But still no air from the vents I said before.
OK the vacuum is good. Make sure the actuators are connected to the arms. Then sometimes the arms become disconnected from their doors. I guess they break inside at the door. It sounds like the panel/demist one might be the problem. Here is a picture of the actuators from the FSM that might help. It is fron a '98 but I think the same as yours.
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