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505069M 07/05
Default Thermostat Settings
Default thermostat settings are shown in table 2 and the
default program is shown in table 3.
Table 2
Default Thermostat Settings
Mode Heat (Perm. Hold)
Heat Setpoint (Perm Hold) 70°F (or 21°C)
Cool Setpoint (Perm Hold) 78°F (or 26°C)
Fan Auto
Filter Reminder OFF
Maintenance Reminder OFF
Equipment Protection Timers Reset Back to Zero
Autochangeover OFF
Table 3
Default Program Settings − Time & Temp.
Programs Time Temp. − Heat Temp. − Cool
All days − A 6:00am 70_F / 21°C 78_F / 26°C
All days − B 8:00am 62_F / 17°C 85_F / 29°C
All days − C 6:00pm 70_F / 21°C 78_F / 26°C
All days − D 10:00pm 62_F / 17°C 82_F / 28° C
Thermostat Output Table
Table 4 depicts the 51M42 thermostat output states for var-
ious input conditions. The following notes described terms
used in the table.
NOTES:
S X = output is activated with 24VAC.
S BBP: outdoor temperature is below balance point
S ABP: outdoor temperature is above balance point
S In all cases, the state of the B terminal is opposite that
of the O terminal
S Data are tabulated for AUTO fan setting. If the fan set-
ting is ON, the G output is activated in all cases
S Upstage timers:
30 minutes (when upstaging from small to large
demand)
15 minutes (HEAT MODE ONLY − when upstaging
from large to very large demand)
S The temperature ranges expressed in the following
definitions of SMALL/LARGE/VERY LARGE" de-
mands are for guidance only; actual temperatures
may vary:
With a SMALL heat demand, temperature is:
below setpoint –0.5F but above setpoint –1.5F
AND 30-minute upstage timer HAS NOT expired.
With a LARGE heat demand, temperature is:
less than setpoint –1.5F
OR 30-minute upstage timer HAS expired.
With a VERY LARGE heat demand, temperature is:
below setpoint –2.5F
OR 15−minute 2
nd
upstage timer HAS expired.
Emergency heat demand (only if emergency heat is
enabled): temperature is below setpoint –0.5F.
With a SMALL cool demand, temperature is:
above setpoint +0.5F but below setpoint +1.5F
AND 30-minute upstage timer HAS NOT expired.
With a LARGE cool demand, temperature is:
above setpoint +1.5F
OR 30-minute upstage timer HAS expired.
Table 4
THERMOSTAT OUTPUTS
Demand Condition
W1 E Y1 Y2 G O
Cooling Demands
SMALL X X X
LARGE X X X X
No Demand X
Heating Demands
With Electric Backup (no outdoor sensor)
SMALL X X
LARGE X X X
VERY LARGE X X X X
Emergency X X
No Demand
With Gas Backup (dual fuel; no outdoor sensor)
SMALL X X
LARGE X X X
VERY LARGE X
Emergency X
No Demand
With Electric Backup (outdoor sensor attached)
SMALL (Above Balance Point) X X
LARGE (ABP) X X X
VERY LARGE (ABP) X X X
SMALL (Below Balance Point) X X
LARGE (BBP) X X X
VERY LARGE (BBP) X X X X
Emergency X X
No Demand
With Gas Backup (dual fuel; outdoor sensor attached)
SMALL (ABP) X X
LARGE (ABP) X X X
VERY LARGE (ABP) X
SMALL (BBP) X
LARGE (BBP) X
VERY LARGE (BBP) X
Emergency X
No Demand