Did you turn off the setting called “WiFi” on the Arc?

That also turns off the radio needed to connect to the Sub.

If you have Ethernet to the Arc you can get an Ethernet switch for about $20 that will split that and allow Arc and Sub to both be connected. Beats hauling the Sub around.

 No. The Arc is a wireless connection. The sub was also a wireless connection which worked 3or 4 times in the last 4 months. If an when it connects to 2.4, the next day is is offline. As I explained, I hauled the sub upstairs to the router for an ethernet connect to see if it worked this way. It did not. Now, Im out of ideas and very disappointed as this sub was expensive

Sounds like time to submit a diagnostic and call Support to have it looked into.

My Arc and Sub have been working since I got them with no issues. Same for my Beam and Sub.

I have also had no problem with tttan Arc -Sub setup since the Arc was laufrtnched.  Faulty hardware seems very likely to be your problem.

Incidentally, the Sub gets its data from the Arc over a 5GHz direct routing, so when they were close together they really should have had no problem. (It doesn't surprise me, though, that with the Arc wireless and the Sub wired in another room you had no success. 

Call Sonos Support. You need to get that Sonos kit looked at.

It connected a few times but says it is always searching for a wifi connection. I can not understand how it set up fine the first time back in May 24, simce then its, dropped the connect, fails to connect and fail to be recognized. 

There are a few routers that struggle with the fact that the Sub connects via the Arc. But a hardware failure still seems most likely. Contact Sonos Support.