Thermostat replacement 101

The three people who occasionally read my blog have heard about my recurring air conditioning woes. The last thing I heard from the A/C guy was that it sounded like a bad thermostat might be the reason for the compressor zoning out at random.

Well, I actually have had a brand-new digital, programmable thermostat sitting around here for months, just waiting for me to quit procrastinating and install the damned thing. So with this weekend's quite moderate temperatures (at least for Tidewater in July) giving me a little leeway for having the A/C shut off for a couple of hours, I decided today might be an opportune time to, yes, quit procrastinating and install the damned thing. (That picture is the actual model I have. Amazingly, it hasn't been discontinued in the time since I bought it.)

So I prepared:

• Gather screwdrivers, drill and bit, wire stripper/cutter, duct tape. Check.
• Read manual from cover to cover. Check.
• Install batteries in the programmable unit and program the cooling cycle¹. Check.
  
• Shut off all circuit breakers with any conceivable connection to the system. Check.

And then I began disassembling the old thermostat. I labelled all the wires (two of which didn't connect to anything, leaving me wondering what they're doing there -- is something disconnected that shouldn't be?), pulled the thermostat plate off the wall, and taped the bundle of wires to the wall so it wouldn't fall into the wall cavity (bet you were wondering what the duct tape was for). And wonder of wonders, the back plate of the new thermostat had mounting holes that matched the old ones, making that drill unnecessary!

Now, I realize this is a low-voltage system, but it still gives me the willies to see wires with slits in the insulation where they don't belong. Whoever wired the old thermostat appears to have known even less about wiring than I do, which is pretty scary. But there was plenty of extra wire to be pulled out of the wall, so anything that was messed up I just cut off and stripped back the end. So with any luck the new thermostat is wired better than the old one was.

With everything connected, I popped the programmable unit onto the wall plate, took a deep breath and turned the circuit breakers back on. Nothing sparked or smoked, so I took an even deeper breath and turned the thermostat to "ON". It worked! It has been merrily cooling and cycling on and off for the last couple of hours, and may actually be set too cool.

Now I cross my fingers and pray that I have cured the compressor's erratic behavior. If so, that just leaves replacing the air handler (which is probably a tad beyond my capabilities).
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¹This model lets you program all days the same, weekdays different from weekends, or for the ultimate in versatility, every day can have its very own program, with four time/temperature settings for each day. This is just a bit too much versatility for me -- being able to set a higher temperature while I'm at work and a lower one while I'm at home would be just fine, thank you, but there doesn't appear to be any way to tell the damned thermostat to just ignore the other two settings. Weekends are even worse; I'd just as soon set it at 72 around the clock. Maybe I could set the temperatures for the extra time settings to be the same as the previous time, e.g., 8:30 AM = 78 degrees, and 5:30 PM, 8 PM, and 11 PM all = 72 degrees. I mean, it doesn't say there's any rule against doing that.