Advanced Temperature Scroll Protector is a temperature-sensitive snap disc in certain scroll compressors. This protects the compressor from discharge gas overheating. Things such as loss of charge, evaporator fan motor failure, or low side charging with inadequate pressure will cause the discharge gas to quickly rise above its critical temperature ~275F. Once the critical temperature is reached, the ASTP snap disc opens and bypasses gas to the suction and causes the scrolls to separate and stop pumping but allow the motor to continue to run. The compressor will continue to run for some time without pumping gas, the motor protector overheats and will open. Depending on the heat build-up in the compressor, it may take many hours for the ASTP to reset. The addition of the Advanced ScrollTemperature Protection makes it possible to eliminate the discharge line thermostat previously required.
Copeland Advanced Temperature Scroll Protector (ASTP) how it works video – https://www.youtube.com/watch?v=BhKNVR-8vDs&t=7s
Application Guidelines for ZB*KCE Copeland Scroll™ Refrigeration Compressors 7 to 15 HP – https://webapps.emerson.com/online-product-information/Publication/LaunchPDF?Index=aeb&PDF=ae1318.pdf