Any A/C Guys on here?

[Reggoh]

Had a general question about Air Conditioners.

I have 2 units in my house and the house is about 5 years old.
I was having a problem with my air handlers in my attic sweating a lot during the summer months.

A friend advised me to stop using the high dollar air filters and start using the cheaper fiberglass ones to allow more air flow. He just advised changing them monthly, which I have been adhering to and this seemed to be working for a while.

One of my units started sweating again and the other is not. I change all the filters at the same time so I don't think that is the problem. Is there anything else I should be doing to maintain my air handlers? Any other problems that cause them to sweat like that?