505232 06/07
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The default is 1.0°F but can be programmed between 0.5° and 3.0°F
in 0.5°F increments. See figure 4 for first−stage heating and cooling
operations.
Figure 4. First−Stage Differential Settings
0°C
100°C
1st-stage ON
Setpoint
+ 0.5°F
No action
Setpoint
1st-stage OFFNo action
0°C 100°C
1st-stage ON
No action
Setpoint
1st-stage OFF
No action
Setpoint
+ 1st-stage diff
− 0.5°F
Setpoint
− 0.5°F
Setpoint
− 1st-stage diff
+ 0.5°F
HEATING MODE
COOLING MODE
2ND STAGE DIFFerential (multistage models only). The low limit
(and default) is 2.0°F but can be programmed up to 8.0°F in 0.5°F in-
crements. See figure 5 for second−stage operation heating and cool-
ing modes.
NOTE − On the 81M28 thermostat, the second−stage operation can
be LOCKED OUT using the balance point settings. This second−
stage lockout will OVERRIDE the operation shown in figure 5.
Figure 5. Second−Stage Differential Settings
0°C
100°C
Setpoint
− 1st stage diff
− 2nd stage diff
+ 0.5°F
2nd-stage ON
Setpoint
+ 0.5°F
1st-stage OFFIf 2nd-stage
timer expires,
then turn on
2nd-stage
Setpoint
2nd-stage OFF
Setpoint
−1st-stage diff
+ 0.5°F
1st-stage ON & reset
2nd-stage timer
Setpoint
− 0.5°F
No action No action
No action No action
0°C
100°C
Setpoint
+ 1st-stage diff
+ 2nd-stage diff
− 0.5°F
2nd-stage ON
Setpoint
− 0.5°F
1st-stage OFF If 2nd-stage
timer expires,
then turn on
2nd-stage
Setpoint
2nd-stage OFF
Setpoint
+ 1st-stage diff
− 0.5°F
1st-stage ON & re-
set 2nd-stage timer
Setpoint
+ 0.5°F
No action No action
No actionNo action
COOLING MODE
HEATING MODE
2ND STAGE DELAY timer (multistage models only). Default delay is
20 minutes but can be programmed from 5 to 40 minutes in 5−minute
increments. If first stage fails to advance the ambient temperature to-
ward the setpoint by 1.0°F in the programmed delay time, then the
second stage is activated (see figure 5).
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