The condenser on a 2004 Pontiac Montana minivan is located
in front of the radiator, typically towards the bottom. It's part of the vehicle's air conditioning system and is a very thin, wide unit. It's often positioned directly in front of the radiator, with the radiator fan blowing air across it to help dissipate heat.
However, accessing it might require removing parts of the front bumper or grille. A repair manual specific to your 2004 Pontiac Montana will give you the most precise location and removal instructions. You should consult a repair manual or a qualified mechanic before attempting any repairs.