90 Riviera-no air from dash vents

i tried searching the forum but couldn't find this problem. on my 90 Riv with 50k, i suddenly can't get air to blow from the vents. it will switch back and forth from heater and defroster just fine. the indicator on the electronic climate control shows the little arrow as if it should be blowing from the vents, but it blows from the defroster instead. i have tried various positions and switching of the electronic climate controls, but i can't get it to work. this will be a major problem for me when it's hot and i need the air conditioner.

a long time ago i had an 87 toronado with this same issue, but when it happened, it would ding and flash "electrical problem". i don't have that light coming on on my Riv though. i don't know if this could be related, but i recently had the valve cover and intake manifold gaskets replaced about 800 miles ago. however, this is the first time i've tried to get fresh vent air and it didn't work. i checked the one vacuum line near the blower and it is connected and there is vacuum.

any ideas? thanks.

Climate control- gotta love it-- look for a vacuum restriction in the plastic nipple manifold that goes into the mode selector module-under the dash right side- there should be about 5 colored vacuum lines on the manifold- - see if you can separate the manifold from the nipples- therein is where the problem usually lies- the nipples turn to gum and plug up the manifold- I have actually opened up the box and bypassed that manifold entirely- the manifold is only there to make initial assembly easy-

It sounds like if you get full flow out of the floor ducts when you select heater and it greatly decreases when set to defrost, that the system is getting vacuum......check the vac line to the a/c defrost valve vac actuator is installed......then set from defrost to vent and see if the actuator moves......if it moves check the linkage to the valve.....if it doesn't move, check for vac, if you have vac, bad actuator....no vac, control head......

I don't know if this system uses vacuum actuators or a vac solenoid box, with a programmer...

the problem seems to be the vent valve upper lever-gm part 3058309. this part is discontinued and not available anywhere in the country from gm. i've searched online but can't find it either. does anyone know where i can get this part???

Junkyard?

i found a 91 toronado at a junkyard, but i don't think they want to tear the dash apart for this little part-i'm trying though. it's only a few inches from the top, so i'm going to see if they will let me cut it out from the top. this is the only lead i have so far.