Honeywell T921A Mode D'emploi page 2

Fig. 2—Vertical mounting of T921A Thermo-
stat on horizontal conduit box. Thermostat
can also be mounted horizontally on vertical
conduit box using accessory adapter plate
and add-on faceplate.
NOTE: ACCESSORY FACEPLATE FOR USE WHEN THE THERMOSTAT
IS MOUNTED HORIZONTALLY. PEEL OFF BACKING AND APPLY
OVER VERTICAL FACEPLATE AFTER MOUNTING IS COMPLETE.
MOUNTING
SCREWS
COVER
WIRING
Be sure all wiring complies with applicable electrical
codes, ordinances and regulations. The power supply must
not exceed 24 to 30 Vac.
Make all electrical connections to the terminals on the
back of the thermostat before mounting the instrument onto
the conduit box. Terminal locations are shown in Fig. 3.
Typical wiring diagram is shown in Fig. 4. Wire the
T921A color-to-color when the modulating motor must
drive the valve or damper open on temperature fall (heating
application). When opposite motor action is required, re-
verse the B and W connections.
Fig. 3—Terminals on back of thermostat.
Fig. 4—Typical wiring diagram for T921A.
SERIES 90
MODULATING
MOTOR
B
1
T
L1
W
(HOT)
T
L2
R
TRANSFORMER
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
2
INTERCHANGE B AND W CONNECTIONS TO REVERSE
DIRECTION OF MOTOR TRAVEL.
69-0828B
BACKPLATE
127246A
ACCESSORY
LOCKING
ADAPTER
SCREW
PLATE
TOP
T921A
M8215
T921A
2
B
W
R
TEMPERATURE SETTING
Adjust the thermostat on the upper right for the verti-
cally mounted model and on the left side for the horizon-
tally mounted model using the setting adjustment knob or
an Allen wrench (see Fig. 5). The device is shipped with the
temperature setting indicator at the center of the tempera-
ture range. Without removing the cover, turn the setting
CONDUIT
adjustment knob, or use an Allen wrench, so the indicator
BOX
is at the desired average room temperature.
IMPORTANT: Do not recalibrate unless the thermostat
continues to be out-of-adjustment after several hours
M9036
of operation.
The T921A Thermostat is calibrated at the factory so
when the room temperature matches the setpoint tempera-
ture, the wiper is at the center of the active potentiometer
winding.
If the thermostat is out of calibration, proceed as fol-
lows (see Fig. 5):
1. Remove the thermostat cover.
2. Turn the thermostat setting adjustment knob or an
Allen wrench until the valve or damper motor is at midpoint.
3. Loosen the indicator lock screw and move the indica-
tor to room temperature. Tighten the lock screw.
4. Replace the thermostat cover. Recheck the calibra-
tion and repeat the procedure if necessary.
Fig. 5—Internal view of vertically mounted
T921A Thermostat (horizontally mounted
model is similar).
B
W
M5989
2
Setting and Adjusting
POTENTIOMETER
WIPER
80
70
60
Calibration
SETTING
ADJUSTMENT KNOB
TEMPERATURE
SETTING
INDICATOR
INDICATOR
LOCK SCREW
BELLOWS
M9082