Ever since I bought my air compressor, a factory-overhauled unit from Campbell Hausfeld, the pressure regulator has been broken in a very specific way. When set to the On position, it would run the compressor automatically as designed, topping up the air pressure whenever it dropped too low. However, it would also do this when the switch was set to the Off position, thus making a mockery of the entire concept of having an On/Off switch. I knew all along what the problem was – a little plastic bit inside the regulator housing wasn't quite long enough to interrupt a set of relay contacts – but the inertia of doing nothing about it made it pretty easy to ignore for a very long period of time.
When we went on trips I would turn it off by flipping the breaker at the fuse panel, which is a well-intentioned idea (avoid burning the house down if the compressor springs a leak) but not particularly a well-executed one (using a breaker as a switch is generally considered bad form). This generally led to simply leaving the compressor in a "live" state overnight, which sometimes caused it to cycle in the wee hours of the morning when the falling temperature caused the pressure to drop below the set point. Although you can't hear the compressor outside our house when the garage door is closed, it is unfortunately sited more or less directly below our bedroom, and is quite audible from in there. It always would wake me up, but I'm a light sleeper so everything wakes me up (here's looking at you, annoying loud neighbor). However, once or twice the sound was even of sufficient intensity to wake Mary from her customary log-like slumber, thus making her quite grumpy indeed. So that was more or less the last straw.
Anyway, I finally got around to replacing the regulator with a $37 part from Pacific Air Compressors:
I'm happy to report that it was a quick and easy job, and now the compressor works as designed in all modalities. Most importantly, I no longer wake up to discover that I'm in the doghouse before I've even found my trousers.