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51M42 SERIES 5/2
HEAT − Using the Heat Mode
Normal Heat Mode
In normal heat mode, both the heat pump and the backup
heat source are used to provide heat. If the thermostat de-
tects that the heat pump is not able to provide enough heat
(as may be the case in very cold weather), then the backup
heat source is activated.
Emergency Heat Mode
In emergency heat mode, only the backup heat source
provides heat Ċthe heat pump is disabled. The backup
heat source is activated only when there is a heat demand.
Enabling Normal Heat Mode
Use the HEAT button to select normal heat mode, emer-
gency heat mode, or to disable heat modes as desired. If
the thermostat is in off or cool mode, pressing the HEAT
button enables heat mode. This is indicated by HEAT in the
lower right corner (see figure 4).
Heat
Prog
Fan
Settings
Cool
Day/Time
Hold
Enter
Normal Heat Mode Enabled
Figure 4
(DOOR
OPEN)
Auto
Copy
70
5:30
70
82
(Outside)
Enabling Emergency Heat Mode
If the thermostat is in heat mode, pressing the HEAT button
enables emergency heat mode (see figure 5). If the ther-
mostat is in normal heat mode when the HEAT button is
pressed, then emergency heat mode is enabled.
62
Emergency Heat Mode Enabled
Figure 5
ROOM
°
75
HEAT SETPOINT
°
HEAT
EMG.
Disabling Heat Mode
If the thermostat is in emergency heat mode when the
HEAT button is pressed, then heat modes are disabled.
This is indicated by OFF near the right side of the display
as shown in figure 6.
75
Heat Mode Disabled
Figure 6
ROOM
°
75
HEAT SETPOINT
°
OFF
Heating Demand
The thermostat must be in either normal or emergency
heat mode in order to properly control the heating equip-
ment. In either heat mode, when the actual temperature is
lower than the temperature setpoint (as shown in figure 7),
the thermostat detects a heating demand and activates the
heating equipment to satisfy the demand. Heating opera-
tion is indicated by a flame icon in bottom right−hand corner of
the display.
72
Heating Demand
Figure 7
ROOM
°
75
HEAT SETPOINT
°
HEAT
When the actual temperature rises above the temperature
setpoint, the flame icon will disappear. This indicates that
the heating demand has been satisfied and that the heat-
ing equipment has been turned off.
Heat pump operation is locked out for 5 minutes after a de-
mand has been satisfied. If another heat pump demand
occurs during this 5−minute interval, the flame icon will
flash; however, the heat pump will not run until the 5−min-
ute delay has elapsed.
NOTE − The heat pump is activated for at least 4 minutes if
no buttons are pressed during the demand interval. The
backup heat source is activated for at least 3 minutes if no
buttons are pressed during the demand interval.
If your system supports 3−stage heating (as does the
51M42 thermostat), you may notice various heating levels
being delivered during a demand.
If a small heat pump heating demand is present, "Lo" is dis-
played in the SYSTEM box; if a large heat pump heating
demand is present, "Hi" is displayed (see figure 8).
65
Large Heat Heating Demand
Figure 8
ROOM
°
75
HEAT SETPOINT
°
HEAT
Hi
Lo