One of the things on the list for October was to replace the a/c filters.  I was going to save it for later in the month; however, the other day one of our units stopped working.  So, that moved it up the list!  Actually, the filter still looked pretty clean; so that wasn’t the problem.  I had never added bleach to the drain pipe, though, because it was a sealed unit.  Since I wanted to try and diagnose the problem myself, I took off the cover and was able to see that the drain pipe was not clogged.  That’s good news.  And I took the opportunity the pour bleach down it while it was accessible.

This isn’t ours, but if you have an access pipe on your a/c unit somewhere, pouring a 50/50 water/bleach solution down it every few months or so could help prevent major problems.
The bad news was that was the extent of my diagnostic ability.  Fortunately, I got a recommendation for a good company from a friend, they were able to come out this afternoon, and the air conditioner is now working again.  (Just in case you were wondering, it was a blown transformer caused by a short in the wire out by the condenser.  My guess is the damaged wire was caused by a lawnmower or weed whacker that got a bit too close at some point in the house’s history.)
Here’s hoping that none of you have repairing an air conditioner on your To-Do List!