What can cause water to leak in on the passenger side floor board and rear passenger side floor board of a 2001 Pontiac Grand Prix only does this when the air conditioner has been on?

Answer 1

air conditioning can cause moisture in the air to condense, especially around vents where the air is moving at high speed. If you live in a very humid area, this could be caused by the air conditioning being so cold that the moisture is condensing out as soon as the cold air meets the warm, damp air. Try running the air conditioner at a higher temperature setting, or on 'normal' instead of 'max'. The more likely senario is that water is leaking in from an area below the windshield under the hood. There is box (under the plastic cover at the bottom of the windshield on the passenger side) that allows air from outside to be pumped inside. If you have this area open you will a see foam seal painted the same color as the vehicle at the base of the box. This so called seal dry rots and GM knows this; however, the seal cannot simply be replaced from what I was told by a windshield replacement shop and a dealer. It is riveted together and must be cut apart and then reassembled. This issue caused the blower motor to seize after the leak corroding the internals of the motor itself.