Sounds like primary and emergency drain are both stopped up.

Thanks. Is this common in a newer unit. Of course it happens on a weekend. I am going to call in a professional on Monday. Is this a big job. Also, my husband said he wants to use his air compressor to blow the outside drain, I don't think he should.

Should be a float switch to automatically cut off system when drain pan fills up past a certain point. It's either defective or you don't have one. Obviously the blockage should be cleared and float switch added or replaced.

Common problem. Sorry for your trouble.

IMO

The installation may have been done incorrectly and it is taken a year for you to notice the leak. It could be as simple as having the correct pitch on the drain pipe.

Do you know how the water is supposed to drain from the attic?

This post was edited by mike_home on Sun, Jun 16, 13 at 9:52

Using a shop vac to suck the line clear from the outside end often works very nicely.

A wet cloth is used to seal the shop vac hose to the drain line end.