Air conditioner and power drawed

My guess is that it won't make a difference. The work done to produce a given amount of BTUs will be the same. People typically will turn the ac fan higher to do the initial cooling and then turn the fan down when the desired temperature is reached. There's no need to turn the ac off - the system will regulate the temperature by cycling the compressor on and off with a clutch.

You can do what you propose to save a small amount of money but you'll pay for it by having a hotter, less comfortable, ride.

The hotter the day the higher the torque load simply because the more work the compressor must do and the longer it will be engaged. At higher revs the power draw WHILE its ON will be higher but it won't be on as LONG. The higher your inside fan speed the more work the compressor must do because you are requiring it to cool more air per unit time. The system turns the compressor on and off as needed to maintain system pressures/temperatures. Turning it off defeats the purpose of the systems controls and just makes the inside of the car hotter. Of course if you are ok with the inside of the car being hotter I guess you can turn it off and on if you want but you won't be saving much gas, not enough to be worth the trouble unless you are running on fumes and are still 10 miles from a gas station. Also, turning it on and off manually will make it much worse at controlling humidity so in addition to having worse temperature control you will also have re-evaporation and worse humidity control.

On my non climate controlled car, I start out fresh by revving rpm and upping fan speed. Low rpm going to take longer to get cool. Compressor may have pressure limit control, don't know. I would not turn compressor off manually, interior gets hot fast. I don't like fixed thermal thermostats used on most. I had one car with adjustable thermostat, not moving vanes.

Greg

The basic manual factory AC system is usually set up to keep the temperature of the cooling coil at about 35 degrees. The temperature of the conditioned air coming out the vents will be as cold as the coil can make it relative to the incoming air temp and the fan speed setting. If it's too cold the temperature "knob" allows some of the warm air from the heater core to mix with the cold air from the cooling coil. You turn the temp knob to get the mix of air that's the temperature you like. If you have automatic AC the automatic part essentially turns that knob (as well as adjusting fan speed) for you based on the temperature you tell the system you want. The old fashioned "under the dash" systems typically used a thermostat that measured the actual temperature of teh cooling coil and when it got down to around 30 degrees it would turn off the compressor... when the temp went back up to perhaps 40 degrees it turned the compressor back on. Generally it had a slower reaction time (longer on cycles and longer off cycles) than how factory systems are setup to cycle the compressor (or otherwise modulate the cooling coil temperature, some use variable displacement compressors.). Having the long "off" cycle time like add on systems do lets the condensed water still on the coil re-evaporate and you get the funny smell of humid water.