... and about 1 gallon of sweat -- and the dog's water dish.  More on that later.

As many of you know, our A/C went out downstairs last night (AGAIN!  3rd time this year) and I was going to try and fix it (or at least diagnose it) myself.  My prior workings on the A/C revealed that, at least electrically, A/C systems are actually extremely simple devices and I had confidence!

It started with Amy telling me around 7-ish that the thermostat was completely dead -- like it had no power.  She was right, there was no power (typically 24 VAC) going to the thermostat.  It was 7pm, so I figured I'd see what I could figure out.  After a simple check of the breaker, I went up into the attic, pulled the cover off the furnace and went to work with the multimeter (yes, the same one my Papa gave me about 20 years ago).  At first I suspected a fuse, but no, both were intact.  Then, maybe the transformer.  No, there was no power into the transformer.  I feared the main control board (pictured) was dead, but I found no power going to the board at all.  Then I suspected the door detection safety switch (which I was pushing over and over while doing all this testing).  Upon opening it up, I found no power going into the unit at all!  I went back downstairs to check the voltage coming off the breaker.  (This is when the dog's water dish was sacrificed.  I mistakenly thought I had two screws left, and the breaker panel cover fell to the floor, the dog's water dish breaking the fall in a spectacular explosion of plastic.)  Alas, the voltage coming off the breaker read live at 120V.  Huh?  The wires in the house aren't that old!

Then I remembered there was actually a switch in the attic that could turn off the power to the A/C unit.  (Groan.)  Did a bird get in there and hit the switch?  A squirrel maybe?  I found the switch, and it was still on.  Despite my doubt that a physical switch (that gets used maybe once every 5 years) could be the root of the problem, I decided to check it out.  Upon pulling the cover off, a piece of plastic fell out.  Interesting.  When I took the switch out, I found a loose wire, not connected to anything.  Aha!  It turns out that the plastic at the back of the switch had cracked (probably upon the original installation) and the contact had completely fallen off (pictured).  The wire to the A/C had likely been just resting against the switch -- time and temperature fluctuations finally disconnecting it.  This is a good reminder NOT to insert wires into the back of the switch, but to use the screw terminals instead.  I raced to Home Depot (as they were about to close at 9pm), bought a new switch for $5.99 and raced home.  Once I installed the new switch, the problem was solved!

Update: Steve and Barbara Arnold have a A/C service website that is chock full of good information if you have A/C problems.  It's somewhat poorly organized and looks kinda 1990s style, but there's good information there and they sell parts for decent prices.  If you get a "pro" to work on your A/C, you might want to stop by this place if you're wondering whether you're getting what you're paying for.