A/C repaired twice still quits

What is your question?

The A/C runs great on short trips around town. Fan works fine. After about an hour in the car on the interstate at (70 mph) there is a strange smell and then the air temperature begins to warm. At first it is cool and finally is as hot as the heater. This first started last summer and took to two different shops. Last one wrote "components freezing replace evap core, receiver drier, expansion valve, and thermistor and all o-rings. Drain evac and recharge." Obviously not the problem. Heater worked fine all winter. Help! I LOVE this car and everyone is telling me it is time to sell.