Nissan Repair: air conditioning, r134, pressure switch

Question
2001 Altima. compressor was clicking on and off rapidly so I replaced the pressure switch and drier.  Now the a/c still turns on and off but it could be on for the entire length of a trip or be off for half the trip then on for the rest.  In a similar question you said the system could be low on R134 but I am afraid to add a can or two if adding too much can hurt.  When I hook up a manifold gauge the low side a/c off reading is between 100-110 and if the compressor clicks on it drops to between 45-50.

Answer
Robert,

Check the high side too and if the reading is under 300 the system is in the normal range.  Did you evacuate the system when you changed the dryer?  If not that is the problem.  If you did and it is cycling that fast it could be overcharged.  You could re-evacuate the system and put in the prescribed amount from the hood sticker.  Something like 2 1/2 pounds.  If it is overcharged the pressure switch will cut the compressor to keep from blowing a line.