The odor is caused by using “Recirculate” continuously.
Respiratory moisture containing bacteria collects on the evaporator coil, then incubates in the heat after the vehicle is parked. The protective coating on the evaporator reacts with the bacteria and produces the ammonia odor.
The easy solution is to use fresh air when possible, the odor will go away in a few days.
There is a GM service bulletin for this issue, it involves installing an after run module for the blower motor to dry the evaporator or switching on the factory feature if equipped. The second step is to apply an evaporator cooler coating to insulate the factory coating.