If you're not having ANY climate control system LEDs or problems, just clear the code and don't worry about it as it's not causing you any problems. If the code then re-occurs with a problem (like you're actually experiencing something wrong with the climate system), THEN I'd think about replacing that sensor but not until then.
As for the 121 MAF meter code, that's also no big deal and most likely not a REAL problem either. The problem with those (in some cars, some years) was that the code was caused by the wiring connector moving too much and caused an intermitant contact prblem, thus sets a code. The cure is simple, use a plastic wire tie and tie the cable back over onto the plug area of that MAF sensor so that the plug can't move from road vibration. Then just clear the code. Do not buy another MAF sensor at this point unless you're having serious drivability problems and that MAF has been determined to be the cause (not at all common with 850s).