Honeywell T651 Manual De Usuario

95C-10903-1

Turn on power. Raise the temperature setting to energize 
the heating contact and break the cooling contact. The 
HVAC equipment should begin heating or stop cooling, as 
appropriate.

NOTE: For T451A and T651A models only, the thermostat 

will call for heat (disable cooling) when the setpoint dial
is at full counter-clockwise position. This setting is the 
phase change point of the diaphragm’s vapor fill and is
independent of calibration. To de-energize the load(s), 
turn off power at the circuit breaker panel, or add a 
separate disconnect switch.

T451, T651 units are calibrated at the factory for accuracy 
at 500 feet above sea level. No recalibration is needed if the
switch operates at the same temperature indicated on the
thermometer.    

The vapor-filled diaphragm sensor is affected by barometric
pressure and altitude. Deviations up to ± 1°F (1/2°C) are 
within normal operation. Control point drops 2°F every 
1000 ft. (1°C/300 m) above sea level. See Fig. 3 for 
recommended action.

1. Remove cover. Set the tab on setpoint knob to the leftmost

radial mark visible on top of the triangular arm that holds
the dual diaphragm sensor (Fig. 4).

2. Without rotating the knob, remove it from the thermostat

by pulling straight out, while holding the base against 
the wall.

3. Now, rotate the removed setpoint knob clockwise by the

amount of temperature error. Each mark on the triangular
arm represents 2°F (1°C) of adjustment. Snap the knob
back onto the setpoint cam. 

Insert pins into
temperature stop 
positions

Range Stops

1. Set thermostat to desired setpoint. Remove cover. 

2. Install plastic dowels supplied (or purchased separately)

into minimum and/or maximum range stop holes on inside
back of cover (Fig. 5).

3. Re-install cover. Check operation of range stops. 

1. Remove cover by pulling straight out.

2. Insert Tinnerman Speed Nut

®

s into slots top and bottom of

thermostat base.

3 Drive Allen screw into Speed Nut until head is flush with

outside edge of thermostat base. 

4. Re-install cover. Lock by backing out Allen screw until

screw body protrudes through cover hole. To unlock cover,
drive Allen screw into thermostat base. 

4. Install the cover. Wait five minutes to let the thermostat

thermally stabilize and re-check calibration.
Do not assume a thermostat is out of calibration until it has
been installed and allowed to operate for several hours.

Honeywell Inc.

1985 Douglas Drive North

Golden Valley, MN 55422

Honeywell Limited-Limitée

35 Dynamic Drive

Toronto, ON M1V 4Z9

4

Elevation 

(in feet)

0 to 2000

2000 to 4000

4000 to 6000

Typical City

Toronto, Ontario

Phoenix, Arizona

Las Vegas, Nevada

Calgary, Alberta

Denver, Colorado

Salt Lake City, Utah

Recommended

Action

Leave as is

Move clockwise

2 to 3 marks

Move clockwise

4 to 5 marks