Easiest thing to do would be to call your installer for service. if you want to attempt the fix yourself, remove the sashes, and there should be a removable vinyl track in the channel. Pry that out and examine the holes where the water should drain. Very possible that they are plugged . If you don't see any visible obstruction, you could always pour a little water in there to see if it drains. If it does not and you can't see anything, then its time to call in a pro.
This is the reason why most pros prefer a welded sloped sill on double hungs as opposed to the pocket style. Unfortunately, you can't really get away from it on sliders, but you don't typically have as many problems because more of the water flow channeling is accessible to clean.

+1

Call your installer first. Might be an easy fix or it could have been hung incorrectly.

Thanks for the tips, I appreciate it. I removed the sliding windows and bottom tracks and cleaned everything out but, interestingly, the inside track does not have weep holes, only the outside track does. The outside track has two weep holes, about 3/4" wide by 1/8" high, but the inside track has none, it is basically a cup. So even when the inside track is perfectly clean, I can pour in cup of water and it just sits, no draining.

I'm now going through Simonton for a warranty issue, but does this sound like a manufacturing error? I thought both slider tracks needed weep holes. Thanks again.

The inner track should have weep holes. Someone fell asleep at the wheel at simonton. Take a 3/16 drill bit and drill 2 holes in the same area as the outer track. Of course remove the track first. Very simple.

While I agree with mmarsel, you should probably have a manufacturer rep come out and take care of that. Not because it is rocket science, but because you'd give the manufacturer a reason to deny a potential warranty claim by drilling into the frame.

Great point HomeSealed. I actually just called simonton and they confirmed the drilling. That said, I would call, and have simonton make a notation of your name/ address as well as the fact that they advised on you creating the weep holes.

Thanks again for the information. SImonton sent their rep out to drill the weep holes and all is good now. Kind of surprising that something like this was missed in manufacturing, but Simonton was quick on the fix so all is well now.

Good follow up.

Glad to see they took care of it.