Nissan Repair: 1998 Sentra Air Conditioning, radiator cap, temp gauge

Question
I have a 1998 sentra 2.0 and when I turn the A/C on the tempature begins to rise and approaches overheating.  The A/C works fine until the temp gets to about 3/4 of the way to overheat and then blows un air conditioned air.  When the temp return to just below horizontal on the temp gauge, the a/c blows cold again until the temp rises and the cycle continues.  when the A/C is off, the car temp appears normal.  Checked both fans and they are operating. Any idea what the problem could be?

Thanks

Answer
Gene,

The thermal load imposed by the airconditioning is too much for the car to take at present.  You say the fans both come on so I will assume that the thermostat needs to be replaced along with a new cap for the radiator.  I would drain the coolant and check the radiator to see if it is getting plugged up.  But, for my thoughts the thermostat and radiator cap need to be changed along with a 50 / 50 mix of antifreeze and demineralized water.