My other thought, is that if it's blowing hot (not just warm, but as if the heat was on) could be in the controls.
If I remember correctly the 'hot/cold' control is connected to two cables, one to adjusts airflow from the heater to fresh, the other adjusts airflow from the AC.
Though I might just be stupid.
Either way, there is a possibility that the AC is kicking in (as he said he can hear the compressor kick in), but the controls are somehow stuck on 'hot', and that that is re-warming the air.
You might want to check controls, or open up the dash to see if the AC unit is getting cold.
My AC just doesn't work, but if you roll down your windows, including the back window, you get a very nice cooling breeze. Keeps me happy in 95 degree/90% humid Wisconsin summers (it gets damn hot and muggy here!)