I completed diagnostics and found the filter 100% blocked. The customer does not have one, he will go get one soon. The condenser coil 100% blocked and I cleaned with water and informed customer how important airflow is. Per no current issue after clearing airflow tech “assumes” system either froze or the condenser high pressure switch opened. To prevent further issues tech suggested regular maintenance. I also suggested to prepare to replace the furnace. The system is operational upon departure.