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Default Thermostat Settings
Default Thermostat settings are in table 1.
Table 1
Default Thermostat Settings
Mode Heat
Setpoint 70°F (or 21°C)
Fan Auto
Filter Reminder OFF (reminder setting = 0)
Equipment Protection
Timers
reset back to zero
Technical Specifications
Thermostat Type
Electronic nonprogrammable thermostat for 1H/1C, heat
pump with electric or gas backup heat source, non−power
robbing applications.
Power Supply Range
18VAC − 30VAC (24VAC nominal), 60Hz
Temperature Display
Display Scale: Fahrenheit or Celsius user selectable (via
DIP switches)
Display range: 35°F (2°C) to 99°F (37°C)
Display resolution: 1°F (1°C)
Display Accuracy: +/−1°F
Temperature Measurement Range
Measurement Scale: Fahrenheit
Measurement Range: 35°F to 99°F
Measurement Resolution: 0.5°F
Measurement Accuracy: +/−1°F
Field Offset: via DIP switches to +/−3°F
Sampling Method: temperature measurements sampled
every 15 seconds. Displayed temperature is the average of
the last four measurements.
Temperature Setpoint Range
Setting range: 50°F (10°C) to 90°F (32°C)
Setting resolution: 1°F (1°C)
Fan Control
AUTO or ON modes.
Backup Heat Source Selection
Electric or gas furnace, selectable via DIP switch #5 (Aux or
Dual, respectively). See also Thermostat Output section.
I/O Relays
All thermostat relays are latching type to minimize power
consumption. See table 2.
Table 2
51M33 Terminal Designations
Connections Description
O Reversing valve, cool active
B Reversing valve, heat active
R 24VAC
G Fan control
Y1 First stage cooling/heating, compres-
sor generated
W1 Auxiliary heating, furnace generated
L Service Indicator
C 24VAC common
E Emergency heat
T Outdoor temperature sensor
connection 1
T Outdoor temperature sensor
connection 2
Equipment Protection Timers
Minimum Compressor OFF time: 5 minutes
Minimum Compressor ON time: 4 minutes
Minimum Furnace ON time: 3 minutes
Minimum backup furnace cycle time (elapsed time be-
tween any furnace activation and the next furnace activa-
tion): 6 minutes.
Minimum elapsed time between any compressor activation
and the next compressor activation: 6 minutes.
NOTE − All protection timers (except the compressor OFF
timer) can be over−ridden if a heating or cooling demand is
initiated or terminated using the UP, DOWN, HEAT, or
COOL buttons.
Equipment Protection Override
Both the minimum compressor OFF timer and the mini-
mum equipment cycle timer can be over−ridden by press-
ing and holding either the HEAT or COOL button down for 4
seconds.
Over−Temperature Protection
Thermal mechanical switch opens W1 at 93°F+/−6°F.
Filter Reminder
Settings of 0 (Off), 1, 3, 6 or 12 months are available. When
programmed time has elapsed, a FILTER indicator is dis-
played.
Balance Point
0°F (OFF) to 55°F, user selectable.
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