Heil unit is a 2000 model. Fan comes on when system is set to both OFF and AUTO. Fan just comes on at will. Heats and cools fine.

Also suspect not cycling properly on cool side as it runs way long and have to manually lower it on thermostat in order to shut compressor off. Thermostat is 3 months old, digital, and made by Robertshaw.

What is the problem?

Thanks.