2002 Chrysler PT Cruiser A/c

"We have a 2002 PT Cruiser. Last year we had to have our air conditioning (Compressor-evaporator-etc) replaced. This year we changed coolant. About 1 week later the A/C started throwing hot air after a 5 minute trip. Once it cools off the A/C works for about the same time or less. I've check a few things. The coolant levels are fine and no coolant on the ground. The thermostat seems to be moving. Any thoughts?"