Ultimate Cooling Tune-Up: cleaned coils, brushed and cleaned traps, added pan treatment tablets to pan. tested and checked all controls, wiring connections. tested temperatures, checked filters. checked refrigerant temperature and pressures, tested static duct pressure. tested blower operation, tested cooling operation to ensure working within manufacturer specifications. Found system to utilize refrigerant R22 that’s no longer manufacture and parts Are no longer manufactured. Found system to be severely low on this R22 refrigerant. Found system functioning with a 4° temperature difference. Normal temperature difference is 18 to 22. Being that the pressure of the refrigerant is low, the temperature will be low causing the coil to freeze up. I recommend the system be replaced as it is almost 28 years old and will not cool.