Home built in 1911. Two AC units ran from one compressor. Exterior unit was a Carrier was 1987, indoor units were Sears of unknown age. Seller said attic unit did not work well. My question is would it ever work well?
I do not think so and seeing the age.
Recommend Immediate replacement by a qualified Installer .
Did one today exterior unit was Lennox 1986
Help me to understand what you are describing your stating one outside condensing unit is feeding two indoor Air handling units each with its own A-coil. Its possible to do what I described but not feasible or economical. The right refrigerant tech could make that operate
Your basically talking about a zoned system which is common on large homes. The most common zone system is controlling a temp in a room or group of rooms by the use of motorized dampers in the supply air duct. There might be two dampers or there might be a 1/2 dozen depending on the size of the home. When ever at least one of the dampers is calling for cooling the outside condensing unit will activate. Each damper motor will have its own temp sensor.
A zoned system will also have a bypass damper from the supply air back into the return air side of the system.
The system you are describing could be described as a zone system depending on how the blowers were activated meaning did each furnace have its own thermostat or were there just one stat controlling both. With two A-coils in use the refrigerant charge would have to be adjusted to accommodate both coils.