I suggested #4 because I notice that on very hot days, the recirculated air is cooler than the no recirculated air, but I'm OK with being wrong. Not knowing the actual flow patterns internally it's difficult to guess which one is most likely the problem.

Ira

 

It is a possibility, that would be the next to test.

 

Yes, recirculated air is always cooler because you are cooling inside air that gets cooler the longer it is on instead of hot outside air. Usually about 5 to 10 degrees cooler and dryer air.

 

Thanks for everyone's input.
As it turns out, another member had a similar problem 11 years ago and asked the group about it. (I did look through the archives last week for A/C problems before posting my original question, but that particular thread did not show up in the search. Sorry.)
A reply in April 2010 from Don06 said, "Not too strange. Freon enters the evaporator from one side and expands (evaporates). If the system isn't full, the expanding freon doesn't fill the evaporator so it only cools part of it. The air that goes through the cold part is the air that comes out the right side."
This was confirmed by a visit to the local garage that does state inspection and other more complicated projects for me (read something I can't do myself). Steve Jr. shook his head knowingly when I asked about low refrigerant only cooling part of the evaporator, saying, "Yeah, I've seen this in Chevys before."
Can't get "Duchess" in for a look-see until later next week, but I will let y'all know what results.

 

So, a vacuum pull to evacuate all the old 134A and a vacuum pull to confirm no leaks then a refill of fresh 134A or 12A .
Keep us posted.

 

As requested, an update:
And, as was posted in 2010 and mentioned above, it WAS the refrigerant level.
I was able to get my HHR into the shop for a look at the A/C system. They evacuated the system, put some leak detector in and then refilled the system with fresh 134a refrigerant.
My mechanic said he had seen this issue before, and the very best way to fix it is to empty the system totally, then refill. Trying to do-it-yourself by just adding refrigerant can backfire and over pressurize the system and damage the compressor unless one has some way to monitor this pressure as new refrigerant is being added.
In conclusion, the little car's A/C system is putting out cold air like it was designed to do, so if any of y'all ever have or come across a car exhibiting this problem, "it's the refrigerant, Stupid."
Thanks to everyone who chimed in with ideas and illustrations. Much obliged.

 

Glad you got it fixed! Now chill ! and enjoy the ride!