  We study condensation and evaporation of particles which repel each other,
using a simple set of rules on a square lattice. Different results are obtained
for a mobile and an immobile surface layer.A two point limit cycle is observed
for high temperature and low pressure in both cases. Here the coverage
oscillates between a high and a low value without ever reaching a steady state.
The results for the immobile case depend in addition on the initial coverage.
