Turning the AC on would probably help if it is summer.
I am not sure just how much cooler an RV refrigerator can be than the surrounding air but I find that I can not get it cool at all when plugged into electric during the day in the Arizona summers. If the air temperature itself were not bad enough there is also the effect of an enclosing metal body sitting in the sun.
During the summer months I can only get it to cool down at night when the temperature drops to the mid 90s and there is no sun baking the RV.