Blend door actuators
 

I have a 1998 GMarq with a blend door issue. The A/C works fine and the heat feed and return are hot indicating a good heater core. When I opened the dash and glove box to repair, the typical electronic gear box is not present. What I have looks like an electro-mechanical bell housing connected to an “L” shaped bracket by 2 small bolts and nuts. This has totally confused me as to proper application. I could use some help/advice from someone with extensive experience. Thanx,

On my 2003 the issue was air always blowing out the defrost, and no change to other ports when pushing selectors on the Temp. control panel. This is a very common issue. Don't know if your model has same arrangement for Climate Control as the 2003. There are many YouTube videos on how to fix this problem. My issue was fixed by me by removing the climate control module from the dash. The mentioned videos shows how to do, and is a pretty easy operation.
There are 4 air/vacuum solenoids in the module. Each one has a .007 o-ring on the stem of its spring loaded plunger. These wear over time and allow the vacuum to leak by, and reduce the power to energize the others. All you do is remove the 4 solenoids, and bend back two metal tabs on each, then replace the O-rings.
A couple of hours time and about $5 in O-rings will save you the many of hundreds of dollars the dealer will charge to replace the whole unit. They will not do the fix, but rather install a whole new unit which is very expensive.