It all depends. There are so many determining factors and variables. Your heat load and insulation plays a huge role. Your ducts should also be of good quality (rating) and in great shape. On a 100 plus degree day in Texas 65 degrees or so may be fine. In a climate of 78 degrees it may be in the lower fifties or even the high forties. It`s best to evaluate the whole system to see if it is performing correctly. The 20 degree split rule is not bad but not fool proof.
The compressor’s discharge temperature can tell the service technician what is going on inside a air conditioning system. The discharge is a reflection of the hottest part of a air conditioning system, and there are limits as to how hot a discharge temperature should be. This article will explore discharge temperatures and their limits. The discharge temperature can be measured by placing an insulated thermistor or thermocouple on the discharge line about 3 to 4 in. From the compressor.
It depends, climate can alter the temperature of your home air conditioning unit. Even the own system of your unit can affect that. You can consult from professionals regarding that matter or you can check some sites like famousacandheat,