i have a 2001 ranger xlt 3.0 v6. when i turn on the a/c when its hot outside, the a/c blows cold, but after a few minutes it starts to blow warm, if i turn the a/c off for a few minutes, and turn it back on , it will blow cold again. i added a can of refrigerant from auto zone, and it didnt make any difference. if its cold outside, the a/c will stay cold. anyone have any suggestions?

 

You will need to get the Pressure gauge set for AC, you can rent them.

Compressor "compresses" refrigerant, this makes it very hot, and increases its pressure, and there is a High Pressure switch that will turn off compressor if pressure is too high.
This hot high pressure refrigerant goes to the accumulator by the firewall, big tube.
There is an expansion valve that releases this hot high pressure refrigerant, this sudden drop in pressure(expansion) causes very very fast cooling of the refrigerant
Cold refrigerant then passes thru the evaporator inside the cab to cool the air in the cab.
This now lower pressure refrigerant goes back to the compressor, and there is a Low Pressure switch on this line, if pressure gets too low switch will turn off compressor.

So too high a pressure will blow off lines, and too low pressure will burn out compressor(refrigerant has oil in it that lubes inside of compressor, if pressure is low then no oil, so burn out)

First thing to do is to see of compressor is shutting off when AC blows warm, if it is then one of the switches is cutting power to compressor.
This could be a bad switch but no way to tell until you test high and low pressure

Google: automotive AC pressure testing

Refrigerant pressure is VERY keyed to OUTSIDE TEMP so pay attention to that detail, and this may be why your AC works better when outside air temp is cooler