So, I've added an hour meter to the Air Charger. You can see the pics below. A couple things to note. Buy an AC capable hour meter obviously, but buy one that is not digital. I bought a digital meter and kind of regret it. Buy a mechanical readout meter so that while the unit is off, you can still see the hours logged. The digital meter only turns on when the pump is on and is off even when the power is on and water pump is working. See below. Also, you'll have to drill a hole somewhere so that you can safely run your meter wires. Make sure that you drill a hole that is not obscured by one of the large capacitors, relay, or power brick. There's not a lot of room to work with, so take note to where I drilled mine.
The blue and brown wires are power to the motor from the control box.
Here's the hole I drilled.
my + from the meter goes to the blue, and my - from my meter goes to the brown.
power on, compressor motor off, meter off.
compressor motor on, meter on. I've only got couple of mins when I took this pic, but I have used it since then and the meter is working as it should
Let me know if you get yours working Dave. Good luck.
Blair