Had the same thing happen while the car was just sitting in the garage for a while(would start it every few days). Never tracked down the blockage, but when I went to replace the expansion valve it was so corroded that it stripped the threads on the evaporator. The valves are known to go bad. Got a replacement evaporator and installed the new valve. Original dryer because it was stuck like chuck and I didn't care to ef up my AC lines at the time. ~10 years ago....