AC compressor power comes from the Switch in the dash, besides the low/high pressure switches it also goes thru the WOT(wide open throttle) Relay, this relay will be in the engine fuse box, and should be closed, passing power to the compressor.
If driver needs extra power for passing or ??, then when the gas pedal is pressed to the floor(WOT) this relay will open cutting power to compressor until gas pedal is no longer at WOT.
I would check this relay.
All AC systems work pretty much the same, in a car or house, your guess is a good one.
Ford trucks, like the Ranger, use a Blend door for the temp select, it moves to adjust air flow thru heater or cooler, it is electric, and does have know issues.
Google: Ford Ranger Blend door
On most vehicles Max AC is just a vent adjustment, it closes the fresh air vent, so cab air which is already cooled is being recirculated, on some models it also closes a heater hose valve in the engine bay, completely cutting any hot coolant flow into cab.
So with an AC system compressor is either ON or OFF there is no Max AC setting for that.
Good page here if you have gauges: http://www.agcoauto.com/content/news/p2_articleid/257