Robertshaw RS4220C User Manual page 6

dF = The differential keeps the thermostat from turning on for small
changes in temperature. When in Fahrenheit the range is 0.5 to 3.0
Degrees. In Celsius the range is 0.5 to 1.5 Degrees. The differential
is factory set at 1.0 °F (0.5 °C). This means that whenever the room
temperature is more than 1 °F (0.5 °C) different from the set
temperature the system will turn on. If the system is turning on too
often, increase the differential setting. Note that a larger differential
will mean the room temperature changes more before the system
turns on.
d2 = Second Stage Differential = Operates with the first stage to control a
second heating/cooling system. This number will be added to the
first stage differential (See: Two Stage Systems). If the first stage is
running too often lower the settings. This will turn the second stage
on to help the first stage. If both stages are coming on too often
then increase this setting to delay the second stage.
dL = Second Stage Delay = This timer starts when the first stage turns
on. It resets when the first stage turns off. If this timer runs out the
second stage will turn on (See Two Stage Systems).
dL E2 = Third Stage Delay = This timer starts when the second stage
turns on. It resets when the second stage turns off. If this timer
runs out the third stage will turn on. Available on RS4320C only.
(See Three Stage Systems).
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