Lots of things effect "coldness" and the thermistor is a good place to start.
Just don't remove it from the fin. It is a fixed temp and the box temp is determined by the air temperature at the level of the thermistor.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW