White Rodgers Heat Pump 90 Series thermostats use a temperature control algorithm to determine the optimum time to activate the second stage or auxiliary heat. The thermostat constantly monitors 1st stage performance and produces a time delay based on the result. The time element of the delay (0-30 minutes) varies depending on the performance of the first stage. As an example, in Heating, assume for the last 2 hours the thermostat is set on 70° and the room temperature is 70° with the equipment using only the first stage of heat. The thermostat calculates (internally) the performance of the system. Since the equipment is keeping the temperature within 1° of setpoint, the thermostat will delay second stage for a longer time if the room temperature quickly changes. Once the second stage comes on, it will come on sooner the next time there is a difference between the setpoint and the room temperature. The thermostat is constantly monitoring the performance of the system and the systems ability to keep the area within about 1 degree of setpoint so even raising the temperature in heating or lowering it in cooling will not always force the thermostat to bring the second stage on quickly. The net effect of the staging program is when the first stage is capable of making temperature the second stage will delay longer. When the thermostat calculates that first stage cannot make temperature in a reasonable time, the second stage will come on sooner. This is a built in function that automatically optimizes the use of additional stages of heat or cool. A thermostat on a Dual Fuel system uses a staging algorithm like the one described above and also turns off the compressor(s) when the furnace is energized.
It is not possible to change the algorithm to prevent the thermostat from staging but staging is always based on performance.