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I don’t find a KIP91S, but do see KBP 91S. Hope this is what you have. If not let us know.
Does the evaporator coil freeze up or the top compartment pan area. If your top is freezing. It is normal to have a layer of ice on the cold plates. But if the coil is frozen, then there is no air movement through it. If that is the case, your glycol system and refrigeration side is working, but the fans are not moving the air over the coil. This is a high end sandwich case, and has a air filter for the compressor. Make sure the condenser and filter are clean. Both internal and external fans have to be working for proper cooling.
I should add here, that bad door gaskets, overloading and addition of warm product will prevent box cooling. Air has to circulate in the box area, but not leak out.
I forgot to ask how you deemed that the box was 91F. If the top is frozen, I don’t believe that the bottom could get to 91F. Verify with a calibrated known to be good thermometer that it is. If you are reading this on the display, you more that likely have a sensor problem.