I think this question falls outside the DIY rules, if not and it needs to be deleted no offense will be taken.
A new system was put in a month or so ago, model numbers/details are...
Furn. AMV90905DX (2 stage/variable speed)
AC. ASX160361 (2 stage)
A new coil and fan powered humidifier was also installed
Thermostat is IAQ Vision Pro (first one the have installed)
The question has to deal with the wiring from the AC unit to the furnace. From all appearances it looks like the wiring for the previous single stage AC unit was left in place, and in turn no wiring to the YLO post on either the IAQ board or the furnance logic board is in place
Now everything does run, however what I'm not sure of is if this setup allows the AC unit to really function as a 2 stage unit or is it just Stage 1 or Stage 2 all the time.
I've tried to keep this short so it is entirely possible more info is needed for advice on whether to phone my installer for yet another time to finish things off properly.