Tech serviced and cleaned unit. Tech found evaporator coil to be severely rusted. Tech did a detailed leak search but could not find a consistent leak. Last tech that came out said the compressor was going from red to caution. Tech megaohmed compressor and found it in the green. Tech faced no other challenges this visit. Unit struggled to get up to Temperature with a delta t of 19 for heat. Tech informed customer about the age of the unit and how the efficiency is not the same as it was before it first got put in. Customer said she will call in for a estimate on a new system.