When replacing thermostat need to know what colors of the wires go to what letters.
Switching from Trane to ritetemp quick start 8022c

Chances are, the answers to all your questions are at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html

Post back if you need help with the details.

When wiring the installer may not have followed mfgrs directions for color code

http://www.ritetemp-thermostats.com/images/8022C_installation_guide.pdf

This is the instructions for your thermostat, you may have to trace wires