Nissan Repair: a/c cycles on off in the heat of the day, nissan frontier, moderate temperatures

Question
We have a 2002 nissan frontier, v6, 3.2 liter. In moderate temperatures the a/c works fine. But on hot days, 95 to 99 degrees, the a/c compressor cyles on/off every 5 to 10 seconds when the truck is stationary, at a stop light or sitting in a parking lot and there is no cool air. The Nissan dealer could not duplicate the problem and the freon pressure checked O.K. The cooling fan is working  fine. The a/c discharge line was replaced 1 year ago but forgot to get the expansion valve replaced then. Could you please help?

Answer
William,

The cycling of the compressor is linked to system pressures which correlate to temperature.  If the system is over charged or under charged the compressor will cycle fast.  Most of the time it is due to under charging.  Now, since you say, it is only doing it when temperatures are high would lead me to think the unit is over charged or the pressure switch is defective.  I would take it to an airconditioning shop and let them know what you have told me along with my thoughts and they should be able to find the problem in short order as it is one of the things I have stated.  Either over charged or the pressure switch is going out.  If there was a blockage in the system the guy at the dealership should have found it.