Air won't divert from vents

[Jon87V20]

Recently, I heard a somewhat loud "pop" type sound under the dash and I just noticed a few days later I can't redirect the air to defrost or anything else other than the vents. I am hearing the vacuum hiss when changing the selector, and I can hear what I think is the door moving and changing positions in the dash. However, it won't redirect.

A few things to note: about a year ago, I pulled the box out from under the glove compartment to change the heater core. I can't remember exactly what happened, but I think I had to glue the blend door because one side of where it pivots had broken or something. It's hard to say because I can't really visualize what it looked like now.

I also recently took the dash pad off and when I did, I accidentally broke the pegs that hold the far right passenger vent tubing up against the outlet. I was able to glue the pegs back on, but it's REALLY difficult to tighten the nuts for those back on. I was only able to get one of the bottom ones on and now the vent doesn't sit tight up against the outlet over there. Not sure if that matters at all, but thought I'd mention it.

I'm taking the truck on a road trip this upcoming weekend so I don't want to start dismantling everything if I don't need to. Any quick things I could or should check that could be hanging it up even though I can hear the vacuum actuating something back there?

1987 Suburban Silverado V20 w/ factory AC (doesn't work / under hood components were removed years ago).

[Mike81K10]

Most likely you have a problem with your vent door inside your box if your cable is intact and working. If your control cable is good, pull your box out so you can make the needed repair. There has been some doors blocked by debris or it failed mechanically.

[MIKE S]

Open the glove box and take the bolts out of the vent adapter on the front of the case. One top center, two on bottom. Slip out the vent adapter and inspect the mode door. The actuator rod goes thru the center of the door and is attached with a plastic mount that can commonly break. Work the mode selector with engine running and see if the actuator moves. Also check the relay rod between the mode door and diverter valve. It may be bound up or disconnected.