T8600D, T8601D AND T8602D CHRONOTHERM IV DELUXE PROGRAMMABLE THERMOSTATS
Using Daylight Savings Time Feature
This feature allows you to change in and out of Daylight
Savings Time with a key press. When the Daylight Time Key is
pressed in the fall, the time will go back one hour. In the
spring, the time will go ahead one hour and the display will
show DST. See Setting the Current Day and Time section for
initial setting instructions.
P+I CONTROL POINT
NOTE: Pressing the Daylight Time Key more than once
within a five minute period will scroll you through
various time options (Example: one hour earlier or
later with or without DST). Pressing the Daylight
Time Key six times in a five minute period will return
you to your original settings.
Fig 13. Proportional temperature control versus P+I
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Displaying the Outdoor Temperature
The thermostat energizes specific terminals depending what
the Fan and System are set to. The LCD will display the time,
room temperature, system and fan selection. Symbols will be
displayed when the heating, cooling or fan is energized. See
Table 10 for specific information.
If your thermostat is equipped with an outdoor sensor, you
can check the temperature at the sensor by pressing i
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NOTE: Not all the thermostat models have all the terminals
listed in the Energize column.
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Table 10. Conventional System Sequence of Operation.
The thermostat microprocessor based control requires that
the user understands temperature control and thermostat
performance. A conventional electromechanical or electronic
thermostat does not control temperature precisely at setpoint.
Typically, there is an offset (droop) in the control point as the
system load changes. This is a phenomenon that most people
in the industry know and accept. Many factors contribute to
offset including switch differential, thermal lag, overshoot,
cycle rates and system load.
Auto Cool or Auto
Cooling O, G and Y
The thermostat microprocessor simultaneously gathers,
compares and computes data. Using this data, it controls a
wide variety of functions. The special proprietary algorithm
Auto Heat or Auto
Heating B and W
O or B
program) in the thermostat eliminates the factors causing
offset. This makes temperature control more accurate than
the conventional electromechanical or electronic thermostats.
The temperature control algorithm is called proportional plus
integral (P+I) control.
When electric heat fan is selected, G is energized and fan
symbol is displayed.
Based on last piece of equipment called (cooling = O or
heating = B) and Installer Setup selection.
The thermostat sensor, located on the thermostat or remote,
senses the current space temperature. The proportional error
is calculated by comparing the sensed temperature to the
programmed setpoint. The deviation from the setpoint is the
As part of the operational sequence, the thermostat
microprocessor also incorporates minimum off time for all
cooling stages. Using the minimum off time assures that rapid
cycling of equipment does not occur, which extends
equipment life. Minimum off times are set in the Installer
The thermostat also determines integral error, which is a
deviation based on the length of error time. The sum of the
two errors is the (P+I) error. The cycle rate used to reach and
maintain the setpoint temperature is computed using the P+I.
The addition of the integral error is what differentiates the
thermostat from many other electronic and electromechanical
thermostats. See Fig. 13.