House is approx 1900 sq feet, replaced all windows cat 5 & heat resistant, dog and myself.

House gets hot, ac fan shuts off. Have replaced circuit and motor over last 2 years.

Still has problems. How much to replace unit

Depending on the age of your existing system, where you live and if you're system is Central Air Only or Central Air/Heat... it has to correctly size as to SEER rating for your needs. If for example you replace your outside condenser with a newer high rated SEER but your still using and old lower rated SEER COIL you will have problems. In terms of BTU's you might need a 5 Ton unit but again... it depends on your area... too large of a unit will cool down quickly but might leave you clammy.

Depending on you specific house design... you might be better off with a two zone system. No point in cooling upstairs bedrooms during the day... or the lower levels during the overnight when you're in bed. Also... make sure your returns are working properly... if not that will add to your woes.

Bottom line... get a few estimates from some local AC companies and go from there.

Stay away from 2 zone systems unless they are also at least 2 stage. I am a FIRM believer in separate systems for each zone. Somewhat more expensive to install, but far cheaper to run.