CNT-SVX12C-EN 19
Chapter 4
Sequence of operations for the
2-heat/2-cool configuration
A Tracer ZN517 unitary controller configured to control a 2-heat/2-cool
unit will operate to maintain the zone temperature setpoint. This chapter
discusses many of the operational sequences the controller uses to accom-
plish this goal.
Power-up sequence
When 24 Vac power is initially applied to the Tracer ZN517 unitary con-
troller, the following sequence occurs:
1. The Status (green) LED goes on.
2. All outputs are controlled off.
3. The controller reads all input local values to determine initial values.
4. The power-up control wait function begins automatically if the config-
ured power-up control wait time is greater than zero. When this func-
tion is enabled, the controller waits for the configured amount of time
(from 10 to 120 seconds) to allow a communicated occupancy request
to arrive. If a communicated occupancy request arrives, normal oper-
ation can begin. If a communicated occupancy request does not arrive,
the controller assumes stand-alone operation.
5. The Status LED goes off.
6. The wait timer expires.
7. The Status LED goes on.
8. If a hard-wired zone-temperature value is not detected, the controller
begins to wait for a communicated value. (This can take several min-
utes [15-minute default] and occurs concurrently with the remainder
of the power-up sequence.) If a communicated zone-temperature
value arrives, normal operation can begin when the power-up
sequence has concluded. If a communicated zone-temperature value
does not arrive, the binary outputs remain off and a Space Tempera-
ture Failure diagnostic is generated (normal operation cannot begin
without a valid zone temperature value).
9. Normal operation begins assuming no diagnostics have been gener-
ated.
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