I have a 2008 3.0 ranger that I bought a few months ago.

Previously the AC compressor would switch on/off within 3-5 seconds constantly, although the air stayed cold when I ran it. (I didn't use it much since I didn't want to damage it assuming I needed a recharge) Over this last weekend my mechanic took a look & said it was low on refrigerant & put up to 1 LB of refrigerant into it. He said he used some dye to test for leaks & found nothing.

The air is is ice cold now & doesn't change temp but I noticed I can still hear the compressor turning on/off fairly frequently still. I've only used it for ~1 hour total since getting it charged but I want to say I hear it on average once every minute while the intervals can vary between (rough guess) 30 seconds- 2 minutes or so. Would this be considered normal? I thought it wasn't supposed to be this frequent but want to see if I'm wrong.

PS. It also seems like the intervals are roughly the same no matter if I use 'AC' or 'Max AC'

 

Low on freon

 

The only difference between max and regular AC is recirculation. Regular AC will let in some fresh air while max won't.

The compressor will shut off for three reasons.
1. The pressure in the system is too low.
2. The pressure in the system is too high.
3. The temperature setting has been satisfied.

Your 15 year old system may be low on pressure causing it to short-cycle. 30 seconds is not all that short, as long as the air coming out of the vents is cold and the system keeps the cab at a comfortable temp,

You will eventually have to replace the compressor, hoses, orifice and seals, but you are not there yet.

 

AC or refrigeration all works the same way whether its in your house or in your car

System works by compressing a liquid, "freon" is generic term, which heats it up and puts it at a high pressure, say 250psi
After compression some of the liquid can turn to a gas, so it goes into a condenser to cool it a bit and turn any gas back into a liquid
This high pressure HOT liquid is stored in Receiver/drier tank
This storage allows the compressor to turn off once there is enough pressure built up

The hot high pressure liquid is slowly released thru an orifice tube(Ford, expansion valve is another term), this slow release of the HOT high pressure liquid cause it to cool rapidly down to about 36degF, in this case you don't want lower than 36degF or you will get ICE build up on AC system, from moisture in the air, even at 36degF you will get water dripping out behind passenger side front time from condensation in the Evaporator housing
(in the case of home refrigerator/freezers it can go much colder than 36degF, lol)

The system has a high pressure switch and low pressure switch, either will shut off compressor
When the system has enough pressure built up on the high side high pressure switch opens and compressor shuts off, or if system was blocked it also prevents high pressure hoses from blowing off, lol
As the high pressure fluid is released slowly thru orifice tube into the Evaporator(inside heater box in engine ) it is cooled down to 36degF, all the air from the fan passes thru the Evaporator and into the cab
Once Air is in the cab there is a "Blend Door", this is the ONLY Temp control for AC or Heat
The Blend door routes the air thru the heater core(HOT) or around the heater core(COLD) or anywhere in between

Once the HOT high pressure fluid passes thru the orifice tube it cools way down and enters the low pressure side of the system, there is also a low pressure switch to prevent the compressor from "running dry", when system gets low on liquid this switch is usually the one that cause the fast cycling
If a compressor runs dry it will burn out in a few seconds, so very important switch, lol
Compressor then re-compresses the returning low pressure fluid

AC only has 2 selections, ON or OFF, there is no temp control for AC as far as the system is concerned
As said MAX AC closes Fresh Air vent, so fan pulls in only Cab air, which is already cooled, so instead of cooling down 100deg outside air, its cooling down 70-80deg inside air so better faster cooling
In some models MAX AC also shuts off coolant flow thru heater core, which is in the cab, so reduces transferred heat from heater core

You home AC and refrigerator/freezer all use the same system, compressor, hot high pressure, slowly released, cold low pressure, and it cycles the same as vehicle systems do