Wait! Stop! Hold the presses!
They're not switching.
Let me explain. When I got it up and running yesterday, I had no way of visually verifying which return discharge had water flowing and which one did not. So today, I did two things. First I just pulled out all 4 tubes leading from the U-hooks hanging on the back of the tank. Of course, this resulted in a ton of air being forced into the water, but it was an excellent means of seeing which tubes had water flowing and which did not. All 4 were flowing. Each SCWD was directing most of the water to, say, the left outlet but nonetheless each right outlet had a small amount of flow.
I let it run like that for a while to see if the SCWDs would switch. While that was running, I drilled a small hole just above the opening of each discharge tube and tied a 4" piece of fishing line. If water was flowing, the line would wiggle furiously. If not, it would be still. It's a simple means of visually verifying which tubes have water flowing and which don't. They were not switching.
Stopped, drained system, unscrewed the lids of ther SCWDs, removed the innards, and manually verified that the impeller was turning. It was. As the impeller turns, it rotates the gate. I manually verified that both gates were in fact rotating as the impeller turned. Re-installed the innards, put lids back on, primed system, and cranked it up. Of course, initially, there was air that needed to be purged from the system, but once all the air was purged, I was able to verify that the SCWDs are NOT switching. The only thing I can think of is that the gate is getting hung up on the hole. So, I called Mr. Musacarello and left a message on his voicemail. It's 9 AM Sunday morning in California right now, so I do not expect a return call for a while. I also just e-mailed him a copy of this post.
In the meantime, I put my ear up to each unit. They are both making a slight steady and rapid chatter like a millions BB's falling to the ground. I assume that is the impeller turning. One of them is also making a steady, but much slower click every few seconds.
PS - I am on St. Simons Island, Georgia, about a 4 hour drive from Augusta.
PPS- It's a 200 gallon tank with a 65 gallon sump.