What causes an roof-top A/C to stop for a while

mine does the same
it will run fine for hrs.
the fan kicks on, then a few seconds later the compressor, which is how
it's suppose to do.
then for some reason the blower fan kicks on, the compressor doesn't when it's suppose to, the blower shuts off. this goes on for, maybe hrs or till i get up and change thermostat threw it's settings, off, heat, cool, auto, back to cool. then it kicks on and my run fine for the rest of the day and night or maybe not