2001 Sunfire a/c air Vent issue

[wvphysics1]

I have noticed some strange behaviour with the vents in my car. The first thing I have noticed is that the lower vents seem to always remain open, even when set to the circulate and forward vent only settings. Also, the forward vents dont seem to put out as much air as they should. If I turn up the blower speed they air increases a little but not much, but I can hear the blower get louder from under the passenger dash. I do not know if these two issues are even related or not. Since the blower gets loud, as in it sounds like alot of air blowing, but doesnt seem to be coming out of the forward vents, I have to wonder if the air is partially blocked.
Any ideas what could be causing the reduced air flow, the inability to shut off the lower vents, or both?
The controls at least partially work because the defroster vents will turn on and off like they are supposed to, and I believe the external vent is opening and closing with the circulate setting.

 

[wvphysics1]

I think the low air flow issue may be occuring after the AC has been on for awhile, and the line leading into the evaporator from the engine compartment has a little frost on it, so this may be the evaporator core freezing up. Any other things to check before I try to check the evaporator? From what i can tell its a pain to get to in a sunfire.

 

[melsg5]

Check the high and low side lines with a gauge. You may have too much gas causing the core to freeze.

 

[wvphysics1]

I actually just did that a little earlier. Static pressure was about 85 psi, when I first turned it on the low side was in the mod to upper 30's, the high side was around 175, after about 15-20 minutes it had settled around 30 low side and 155 low side. It was about 80 degrees and 60% humidity. The drop was a bit strange and the high side seemed low, but the behavior didn't seem to indicate anything like any problems I coukd find described online. The "temperature conversion" on the gauge showed above freezing, at least at the time by I know earlier in the day after drivng home there was frost on the low side tube. Tomorrow I'll check again after driving home from work.