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51M35 SERIES 5/2
Technical Specifications
Thermostat Type
Electronic programmable thermostat for 2−Stage (gas or
electric) Heat/2-Stage Cool, non−heat pump, non−power
robbing applications.
Power Supply Range
18VAC − 30VAC (24VAC nominal), 60Hz
CAUTION
24VAC is present on the terminals of the thermostat
bracket. If removing the thermostat from the wall,
use caution and avoid touching any of the connec-
tor terminals on the wall bracket.
Also, when working with the thermostat dip
switches, use a non−conductive tool and take cau-
tion to avoid making any contact with the circuit
board, its imprinted circuitry and its connector
prongs.
Temperature Display
Display Scale: Fahrenheit or Celsius user selectable (via
DIP switch; see figure 18)
Display range: 35°F (2°C) to 99°F (37°C)
Display resolution: 1°F (1°C)
Display Accuracy: +/−1°F
If the Fahrenheit/Celsius display must be changed, use a
plastic, non−conductive tool to push the dip switch to the
right position (see figure 18).
F/C (Fahrenheit/Celsius) switch
shown in Celsius position
Figure 18
Changing Fahrenheit/Celsius Setting
1
2
3
4
5
6
PLUG IN (Use Care To Avoid Bending Prongs.)
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)
Smart Setback Recovery (via DIP switch #6)
Smart Setback Recovery (SSR) affects the way the ther-
mostat responds to program events. If SSR is disabled, the
thermostat will react to a program event at the time the
event occurs. However, if SSR is enabled, the thermostat
will react to a program event before the event occurs such
that the desired temperature is reached at the time of the
event, not after.
Fan Control
AUTO or ON modes, gas or electric heat compatible via
DIP switches (also see Thermostat Output section).
I/O Relays
All thermostat relays are latching type to minimize power
consumption.
Table 4
51M35 Terminal Designations
Terminal Description
R 24VAC
Y1 First-stage cooling
W1 First-stage heating
Y2 Second-stage cooling
W2 Second-stage heating
G Fan control
L Service Indicator
C 24VAC common
Equipment Protection Timers
Minimum Compressor OFF time: 5 minutes
Minimum Compressor ON time: 4 minutes
Minimum Furnace ON time: 3 minutes
Minimum furnace cycle time (elapsed time between any
furnace activation and the next furnace activation): 6 min-
utes.
Minimum elapsed time between any compressor activa-
tion 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 and W2 at
93°F+/−6°F.
Filter Reminder
Settings of Off, 1, 3, 6 or 12 (months of fan run time) are
available. When programmed time has elapsed, a FILTER
indicator is displayed.