In that case it is likely that the evaporator iced up. Ours did that on a long trip as well. The solution that we found was that when air flow starts dropping off like that, turn the A/C off, and leave the vent running. The ice will keep the air cool. Air flow will start coming back as the ice melts, and should be at full force rather quickly. When it started getting warm, we kicked the A/C back on, and all was well.

When it gets down to temp, it should start backing the fan down, but I doubt that was a factor here. It will start drifting the air warm on you usually before that happens.

Your A/C seems to be working great, perhaps a little too good. I would just let it be.

I will try vent mode when air flow is reduced.

I am pretty sure that it'* freezing because of the continuous run of compressor.
The system should cycle on & off.
Low Pressure switch or bypass in wiring?
The system was recently tested on both high & low with gauges, all is up to speed there.

It could also be a drain issue. Have you checked the drain tube at the bottom area of the firewall?

I know it drips water below car when I turn car off Mike. Will try to locate it and make sure water is coming out of the tube.
How To Clean it? Use coat hanger to make sure it is not blocked?

What happened to the old school days with this car and AC ?
I stopped by the local pro shop and he went to look for the low pressure switch.
Ya not there. So he does reference on computer and informs me the AC & Clutch cycling is controlled by PCM though pressures in conjunction with the Pressure Transducer that relays variable voltage back to PCM ~! WOW!
Sound like when it gets too cold vent mode is it!!!
Oh here is the insulation run left of serpentine belt I did. MY AC rocks now.

I have seen a couple cars in the junkyard have insulation wrapped around the dryer also. Might be something for you to look into. Couldn't hurt anything right?

No need to insulate the drier on my car !
It get so white & icy cold, I want the under hood temps to melt the ice off of it, so it does not freeze up!