This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
Jim Zimmerman says: Short cycling [the a/c unit going on and off every
five or ten seconds) would allow it to cool, but not very well. An
independent shop immediately found that the first shop put on a
defective expansion valve in their attempt to repair it. Also, the low
pressure switch was bad. Mine would only act up intermittently. One day
it would cool just fine, the next day it would short cycle again.