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T921A,B,E-G Proportional
Control Thermostats
T921 Thermostats provide 3-wire, low voltage
proportional control for Series 90 (135 ohm) valve
motors, damper motors, and balancing relays in
heating or cooling system applications.
nn T921A nn T921B nn T921E nn T921F nn T921G
n Accessory faceplates available for horizontal mount-
n A bellows element adjusts the potentiometer slider
ing of T921A,B,E models. to regulate motor operation.
n COOL-HEAT changeover switch in the T921B. n Various temperature
Summary of the content on the page No. 2
T921A,B,E-G SPECIFICATIONS • ORDERING INFORMATION Specifications ® TRADELINE MODELS THERMOMETER: Bimetal. Scale ranges T921A only: ® TRADELINE models are selected and packaged to 45° to 75° F [7° to 24° C]. All other models: 60° to 90° F provide ease of stocking, ease of handling and maximum [16° to 32° C], 15° to 35° C [59° to 95° F]. T921A is also ® replacement value. TRADELINE model specifications available with a blank cover and no thermometer. are the same as those of the standard models ex
Summary of the content on the page No. 3
T921A,B,E-G SPECIFICATIONS 7640HX Averaging Element Mounting Kit: For mount- Fig. 1—T921 approximate installation dimen- ing in existing installations where access to the duct sions in in. [mm]. is impractical. Q615A Enclosure: To protect the device when mounted ACCESSORY ADAPTER PLATE (127246A) FOR SETTING MOUNTING ON HORIZONTAL CONDUIT BOX ADJUSTMENT outside; splash proof. KNOB HORIZONTAL CONDUIT BOX 801534 Calibration Wrench. FOR VERTICAL 107324A Bulb Holder: For mounting the bulb in a duct.
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80 70 60 60 70 80 90 HONEYWELL T921A,B,E-G INSTALLATION Installation ADD FACEPLATES FOR HORIZONTAL MOUNTING (T921A,B,E ONLY) CAUTION ! T921 models are shipped with a faceplate for vertical Disconnect power supply before installation to mounting. When mounting the T921A,B,E horizontally, prevent electrical shock and equipment damage. see Table 2 to order the faceplate with the appropriate scale. NOTE: Do not mount the T921F,G horizontally. WHEN INSTALLING THIS PRODUCT… TABLE 2—ACCESSORY FACEPLA
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R B W B W R R B W B W R RBW 80 70 60 60 70 80 90 HONEYWELL T921A,B,E-G INSTALLATION Fig. 4—Vertical mounting of T921A,B,E-G Fig. 5—Terminals on back of thermostats. Thermostats on horizontal conduit box. TOP TOP T921A,B,E Thermostats can also be mounted horizontally on vertical conduit box using add-on faceplate. (Do not mount T921F,G horizontally.) NOTE: ACCESSORY FACEPLATE FOR USE WHEN THE THERMOSTAT IS MOUNTED HORIZONTALLY. PEEL OFF BACKING AND APPLY OVER VERTICAL FACEPLATE AFTER MOUNTI
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T921A,B,E-G INSTALLATION • SETTING AND ADJUSTING Fig. 7—Typical wiring diagram for T921B. Fig. 9—Typical wiring diagram for T921F. SERIES 90 MODULATING T921F MOTOR SERIES 90 B B MODULATING B 1 T MOTOR T921B 2 L1 2 W W (HOT) B B B T L2 1 T R R W TRANSFORMER L1 W W (HOT) T L2 W R R 3 R TRANSFORMER 2-POSITION AUXILIARY ACTUATOR SWITCH B 1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. W 2 INTERCHANGE B AND W CONNECTIONS TO REVERSE DIRECTION OF MOTOR TRAVEL. 1 CLASS 2
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T921A,B,E-G SETTING AND ADJUSTING • OPERATION This switch energizes a heater that offsets the ther- Fig. 11—Internal view of vertically mounted mostat approximately 10° F [6° C], lowering the T921 (horizontally mounted model is similar). temperature for night operation. Leave this switch in the OFF position for normal operation; turn it to the POTENTIOMETER ON position for lower night time temperature. WIPER SETTING 1 ADJUSTMENT KNOB CALIBRATION IMPORTANT: Do not recalibrate unless the thermosta
Summary of the content on the page No. 8
T921A,B,E-G OPERATION␣ T921B Fig. 13—T921G auxiliary switch operation. 1. Place the changeover switch (see Fig. 11) in the HEAT position and follow steps 1 through 3 of the T921A TEMPERATURE procedure. TEMPERATURE 2. Move the switch to the COOL position and repeat FALL R-B MAKES steps 1 through 3 of the T921A procedure. 1˚ F [0.5˚ C] +2.5˚ F DIFFERENTIAL [+1.5˚ C] 3. If the valve or damper responds properly to the R-W MAKES thermostat, move the setpoint to the desired temperature. TEMPERATURE R
