Hi again! So, none of the experts here have any ideas about this? Am I nuts for thinking this is caused by an R410A refrigerant leak into the condensate drainage pan on the air handler in the attic?

 

Its normal!

 

All kinds of funny things can grow in the condensate pan and drain. Also fine dust could get through the air filters, collect on the coil, wash off the coil and out of the drain pan, finally down the eaves drain.
Soon you will know, if its a refrigerant leak it should be oily to the touch.
keep us posted.
What is the climate?
Regards Teddy Bear

 

and a combination of dust, dirt, roof shingles all laying in the gutter mixing with the water.

I see it quite often here.

 

Hmm. In reply to both pecmsg and teddy bear: how oily to the touch? The water coming out and pooling slightly does seem to have an oily sheen on it but maybe I’m imagining it. Also, this did not start happening until about 4 weeks after the system was installed, and it never happened with my previous system. Plus, the white stuff doesn’t seem to scrub off, and when I moved the down spout, the white stuff reappeared in the new area. So far I don’t notice any change in cooling performance, and the climate here on Long Island, NY has been normal for summer: 75 - 95 with humidity from 50 to 90 %. Dew point this week is in the upper 70s. I keep the inside temperature set to 74 in the daytime and turn the system off at night.

 

oily sheen and white goo is often the sign of bacterial growth.

a POE leak that big would leave a huge mess inside the coil box. have the tech check that.

 

The White goo/slim is called Zooglea. I hate that stuff. It seems to be more prevalent on systems that have evap humidifiers.

I've had some promising results using my-calgon Gel tabs.

 

While the suggestions above may be correct, I think there is a good chance that it is residual oil on the fins from when they were stamped into shape prior to assembly of the coil. I used to run a coil department for a large manufacturer. The water in our test tank was always milky white from the stamping oil that rinsed off there. Even after going through the tank there was still residual oil on the fins that washed off after a few weeks of operation. If we were sending a coil straight to a lab for performance testing we had to degrease it first because the residual oil would cause some extra condensate to stay in the coil and reduce performance.

I doubt that coils for residential product go through a water bath, as they are usually leak-checked with helium. Look in your air handler and see if you see anything obvious. If you don't, I would give it a few more weeks.