The cold air return from the evapoator is sweating excessively. What may be wrong?

Answer 1

It is very hot outside. As long as your A/C is putting out cold air, and isn't freezing up, it will be okay. It is normal for it to sweat a lot, especially in extreme temperatures.

Answer 2

It may be nothing as long as you know it is just sweat. The humidity of the ambient air may just be higher recently.

Answer 3

You might want to consider insulating the duct(s) in question.

Your system will be more efficient (cheaper to run)- and you will avoid whatever problems the condensation is causing or will someday cause.