The air conditioning is great for the first 2-3 hours of high speed long distance driving, but then slowly starts blowing warm humid air and the fan speed slows down quite a bit. If I stop for a 1/2 hour or just turn it off for a 1/2 hour while driving, and then turn it on again, it is fine.

Sometimes, it won't happen again on the same trip. It seems like the faster I drive, the less likely it will occur.

I purchased the car new and the air conditioner is used sparingly.