2002 Cadillac EL Dorado How to clear or fix code 1312

The temp sensor is in the high side line, by the plastic clip that holds the line down near the center firewall. It may or may not be a sensor, it could be wiring. You should have 5 volts on one wire, and the programmer grounds the other. Both the low temp, and high temp are the same and can be switched to see if fault follows sensor. I don't recommend or endorse adding freon yourself, if you have to ask how. It is dangerous, and can cause more problems with the system if done improperly. A parts store might sell you the do-it-yourself kit, though. Clearing/reading codes-push off and passenger warmer until a segment check displays, and codes follow. Fan down will scroll modules and options, fan up will select. Go to ACM, or ACP clear codes.