Operating State Sequence Chart; Startup Control; Before Startup - McQuay MicroTech II Operation Manual

Figure 7: Operating State Sequence Chart

Operating State Sequence Chart

Operating states and the transitions between them help to
describe the unit sequences of operation. Figure 7 shows all
of the operating state transitions that can occur as a result of
normal control. Depending on the unit options, some operat-
ing states may not apply.

Startup Control

A rooftop unit can startup and run for a variety of reasons.
Examples are the internal time schedule function, an external
time clock signal, a tenant override signal or the unoccupied
heating (night setback) and cooling (night setup and purge)
functions. Regardless of the reason it is started, the unit
always transitions through a "controlled" startup sequence
before allowing temperature control to begin.

Before Startup

Table 29: Programmable Parameters
Keypad/Display ID
Menu Name Item Name
- -
Timer Settings Start Init = 3 min
When the controller receives a startup command, its operat-
ing state changes from the Off to Startup operating state.
64
Parameter Name
Minimum Inlet Vane Position
Limit
Startup Initialization Timer
During the Startup operating state, the Fan Operation Output
(MCB-BO3) is closed to indicate that the fans are about to
start. On units with return fan inlet vanes, the vanes are
driven open to the non-adjustable Minimum Inlet Vane Posi-
tion Limit. This limit is 17% and is not adjustable. The Min-
imum Inlet Vane Position Limit assures that the return fan
does not start with a completely blocked airflow path. On
units with a return fan VFD, the VFD remains at 0% speed.
The unit remains in the Startup operating state until the Star-
tup Initialization Timer expires.
Note: On 100% OA units equipped with gas heat, the
Startup period may last longer than the period
defined by the Startup Initialization Timer if heat is
required at unit startup. For a description of this
special 100% OA gas heat startup sequence, refer to
Figure on page 82.
Caution: The Startup Initialization Timer should be set so
that the Startup operating state lasts long enough
to allow any field-supplied equipment (such as
isolation damper sets) controlled by the Fan
Operation Output (MCB-BO3) to prepare for fan
operation.
OM 138