The KRCS01-4B 4 Pin Remote Sensor Kit is Recommended for Ceiling Suspended (FXHQ) and Ceiling Concealed Types (FXDQ, FXMQ, FXSQ, FXFQ, FXZQ) which often Result in a Difference Between Setpoint Temperature and Return Air Temperature, in Ducted Style Units with an Open Return-Air Plenum Environment or where Outside Air is being Mixed at the Unit's Return Air Opening, or where High Ceilings Result in Temperature Stratification between the Occupied Zone and the unit's Return Air Opening