Just judging from the amount of air coming from dash vents in normal AC and Max AC, the volume of air is much greater in the Max position. What could be restricting the volume?
I do wonder if maybe it is not getting external air for some reason. I've eliminated the posibility of it being back pressure when trying to pull external air by rolling windows down.
Is there a troubleshooting procedure to check blend/diverter door functions?

 

Have you checked the cabin air filter? If it's clogged, it will impede the airflow into the fan, which may be what you are experiencing.

Doug

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The 2001's never had a cabin air filter. However, have you checked inside your cowl for blockage by leaves and stuff?

 

It is normal for air volume in MAX to be substantially higher. You don't have a problem.

 

I don't notice any difference in air volume between normal AC with the interior air recirculation deal on and max AC. All max does is set it to interior recirculation (which makes it blow harder). If anything, max AC should give less volume because it sends air out of all the vents instead of just the "face/upper body" ones.

That being said, OP, does the interior recirculation button change anything for you?

 

Might check cowl, but think that unlikely since vehicle always garaged and only 50K miles.
Different concern, but condenser was very clogged with bugs and it took multiple cleaning efforts to fix that.

 

I've seen some that Max position automatically puts fan on high, but not different than setting fan to high. If cabin was well sealed, that might happen along with a significant increase in noise. I was told by GM that they were required by law, possibly because of CO concerns, they were required to have a minimum leakage rate. An 11 Lacrosse is so leaky that you had to run in outside air position, CAF in path, to reduce pollutants entering from other leaks.

That is why I also tested with windows open, just in case there was an issue with the two big external vents located on lower back wall of cabin.

 

This is 01 without EATC. No such button. Recirculate only occurs in Max position. Dash controls remind me of most Ford products from early 80's on till at least early 2000's.

Is there a diagram available that shows vacuum logic from control head to doors? I'm guessing that it would be easy to send vacuum down each line to check door functions.
This was my Dad's last new truck and for all I know it might have been like this from day one.

 

The only thing that changes from MAX to A/C is the inlet door position. In MAX, it recirculates (far less blower resistance). In A/C, it admits air from under the windshield cowl and expels it through ether open windows or the outlet vents.

 

This is essentially my understanding as well, which explains why it blows more, especially if you don't have a recirculate button. Not having the recirculate button makes complete sense for max to be more powerful. I thought my dad's old 03 had one, so my apologies on that.

 

Your dad may have had EATC instead of manual controls. My 03 is manual control, no button, just MAX and A/C.

 

Ahh well if my mom hadn't plowed the truck into a tree 5 houses down on Father's Day a few years back, I'd probably be able to check . . . oh well! It was a Lariat Screw, so it likely had it if it was available.

 

How many doors and positions?
I checked the other control positions and all seem noisier than they should be compared to Max AC, as if something is restricting air flow, which is why I ask that question.
And whether blower can be removed without tearing everything else loose, for the purpose of looking into case and checking door movement.

 

Project seemed to hit it, except the part about far less blower resistance in Max AC. Likely there would be some resistance added in a non-recirculating mode, but not with windows open.
And as to a recirculate switch, that would have the same purpose as switching to Max AC from my understanding of similar setups. The only vehicle I've ever seen with this type of setup that had similar issue was a late 90's Sable that had a CAF tucked up in the cowl and it was completely matted over with debris and mold growth. This vehicle is not supposed to have a CAF and the location for adding one, bottom of HVAC case, does not have it. Pretty hard to imagine anything big enough being sucked past the inlet grill below windshield and plugging that large duct.

 

I don't know how the AC systems work exactly, but I don't notice having the windows open or closed having any effect on mine at all. I have them down almost every day too.

I agree that recirculate having the same effect as max, that has been my observation.