You might want to measure the vent temps with the CC set to "Lo." You should be seeing vent temps in the low 30's running down the road. If not, you're probably low on freon, hence the frequent compressor cycling as the low pressure switch kicks in and kills power to the compressor.

if you have a blockage in the lines pressure can build till the compressor shuts off then the pressure dissipates and it turns on again...

what I'm trying to say is pull a vacuum on the system before you add freon, that way your sure not to over charge it..

I'd start with a temp reading at the vents and depending on what I get there, hook up the gauges and get a high side and low side reading.

Of course that's if there is actually a problem to begin with!