Trane LO - Manual (Page 71)

UNT-IOM-6 71
Tracer ® ZN.520
to expose the damper stop screw on the control panel end. Relocate
the stop screw to the appropriate position. Then loosen the stop
screw wingnut and adjust the linkage.
Economizer Damper
With a valid outdoor air temperature (either hardwired or communi-
cated), Tracer ® ZN.520 uses the modulating economizer damper as
the highest priority source of cooling. Economizer operation is only
possible through the use of a modulating damper.
Economizing is possible during the occupied, occupied standby,
unoccupied, and occupied bypass modes.
The controller initiates the economizer function if the outdoor air
temperature is cold enough to be used as free cooling capacity. If the
outdoor air temperature is less than the economizer enable setpoint
(absolute dry bulb), the controller modulates the outdoor air damper
(between the active minimum damper position and 100%) to control
the amount of outdoor air cooling capacity. When the outdoor air
temperature rises 5 F above the economizer enable point, the control-
ler disables economizing and moves the outdoor air damper back to
its predetermined minimum position based on the current occupancy
mode or communicated minimum damper position.
Table 25. Relationship Between Outdoor Temperature Sensors
and Damper Position
Outdoor Air Temp.
Modulating Outdoor Air Damper
Occ. or Occ. standby Unocc.
Occ. bypass
None or invalid Open to occ. Open to occ. Closed
min.pos. standby
min. pos.
Failed Open to occ. Open to occ. Closed
min.pos. standby
min. pos.
Present and econ. Economizing: Economizing: Open and
feasible min pos.-100% between occ. econ. only
standby min. when unit
pos.-100% operating,
closed
otherwise
Present and econ. Open to occ. Open to occ. Closed
not feasible min. pos. standby
min. pos.