Honeywell T921A Mode D'emploi page 3

In the T921A, a vapor-filled bellows moves the potenti-
ometer wiper by expanding or contracting in proportion to
temperature changes. As the wiper moves, the appropriate
motor winding is energized, opening or closing the valve or
damper to compensate for the temperature change in the
controlled area.
After the thermostat is wired and mounted, check to be
sure the T921A Thermostat and controlled equipment are
functioning properly. Before proceeding, allow from one to
three hours for the system to stabilize.
1. Set the temperature setting indicator to room tem-
perature by using the setting adjustment knob, or an Allen
wrench (see Fig. 5). The valve or damper motor should be
at midpoint.
Operation
Checkout
3
2. Move the setpoint 3° C [5° F] below room tempera-
ture. In a heating application, the valve or damper should
close; in a cooling application, the valve or damper should
open. If the valve or damper is driven in the opposite
direction, interchange the wires at the B and W terminals.
NOTE: If a proportional action limit control is used, the
motor may not move the damper or valve all the way
closed or open. Check the limit action after interchang-
ing the wiring.
3. Move the setpoint 3° C [5° F] above room tempera-
ture. In a heating application, the valve or damper should
open; in a cooling application, the valve or damper should
close.
4. If the valve or damper responds properly to the
thermostat, move the setpoint to the desired temperature.
69-0828B