The low side pressure doesn't tell you anything except that the compressor is shutting on and off at the correct low side pressures.

If this is happening with the fan set to "high" with the car sitting in the hot sun, on a hot, humid day with the windows open, you have a problem.

The quick cycling can also be indicative of a cool interior, low charge, plugged orifice, low ambient temp, low outside humidity, or a few other things. If the output temp from the vent is cool and doesn't vary radically, it might be behaving normally given the outside conditions.

Usually people who notice this kind of thing notice because their system behaves differently all of a sudden. If this is the case, you really need to measure the charge in the system, or measure the high side system pressure. A lot of newer R134 a/c systems don't have high side pressure ports (and you'd need a gauge manifold set) so you would have to actually have a shop measure the charge in the system and top off if necessary.
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chris herbst, near chicago