[Fat Charlie]

Obviously, cycling the AC as needed is the most efficient way to use it, but I found the assumption (For greater efficiency, switch it on when under light engine loads or deceleration fuel cut off and off when under moderate/heavy loads.) to be dead wrong.

Using GPH as a measurement, I saw that it increased more while gliding than when the engine was already under load. This wasn't just by percentage but by actual increase amount. For example (and pulling numbers randomly out of my ass here) say I was gliding at 0.4 gph and hit the AC which brought me up to 0.8 gph. The compressor then added 0.4 gph to what I was already using anyway. Under load at 4.0 gph the AC only brought me up to 4.2 gph. So while gliding the AC costs me 0.4 gph but under load it only costs me 0.2 gph. Add that to the fact that I have to leave the engine running during the glide if I want to run the AC, then in practice it's costing me 0.8 gph instead of the 0.2 gph that it costs when I need to be running the engine anyway.