Technical Guide
Full Digital Module
11
Modes of Operation
NOTE: See Unit Confi gurations Chart on page 10 for more
information about compressor staging.
Digital Stage 1 / Digital Stage 2
On units with two Digital Scroll Compressors, the fi rst compressor (A1)
will be designated as Digital Stage 1 and the second compressor (A2)
will be designated as Digital Stage 2.
On units with four Digital Scroll Compressors, there may be instances
where compressor numbers on the module do not correlate with the
mechanical compressors’ numbers. Therefore, Digital Stage 1 refers to
the fi rst set of Digital Scroll Compressors (A1/B1) that will stage on
together and Digital Stage 2 refers to the second set of Digital Scroll
Compressors (A2/B2) that will stage on together. Please refer to AAON’s
wiring diagram for specifi c wiring of the unit.
Off Mode
The Full Digital Module will be in the Off Mode when no signal is
being received from the VCM-X Modular series controller to run the
compressors.
Cooling Mode
When a Cool Signal is received, the Full Digital Module will go into
Cooling Mode. At this point, Compressor A1 (and B1*) will energize and
Digital Stage 1 Analog Output will modulate as necessary to maintain
the Supply Air Temperature at the Active Supply Air Setpoint that is
broadcast from the VCM-X Modular series controller.
When Digital Stage 1 reaches 100%, a stage up timer is started. If Digital
Stage 1 stays at 100% for the Stage Up timer, Compressor A2 (and B2*)
will energize and both Digital Stage 1 and Digital Stage 2 outputs will
go to 50% and begin to modulate together.
If both systems are energized and they go below 30% and the Supply Air
is below the Supply Air Setpoint by the Cooling Stage Window value,
the stage down timer is started. If the systems remain below 30% for
the duration of the stage down timer, Digital Stage 2 will deactivate and
Digital Stage 1 will go to 60%. Digital Stage 1 will stage down if it is
at 0% for the duration of the stage down timer.
* If confi gured for 4 modulating compressors.
Heat Pump Heating Mode (Air to Air)
Heating Mode works the same as Cooling Mode except the Reversing
Valve is switched and the sequence is opposite. Compressors modulate
up when below the Heating Supply Air Setpoint and modulate down
when above the setpoint.
Dehumidifi cation Mode
In Dehumidifi cation Mode, compressors will be controlled to maintain
the Suction Pressure Temperature Setpoint. Digital Stage 1—Com-
pressor A1 (and B1*) will modulate up to 100% before Digital Stage
2—Compressor A2 (and B2*) can be energized. When Digital Stage 2
is energized, Digital Stage 1 will be locked at 100%.
* If confi gured for 4 modulating compressors.
Defrost Mode
In Defrost Mode, if only Digital Stage 1 is energized, it will go to 100%
and the reversing valve will deactivate. If both Digital Stage 1 & Digital
Stage 2 are energized, they will both go to 100% and the reversing valve
will be deactivated. The duration for Defrost Mode is determined by the
VCM-X Modular series controller.
NOTE: Defrost Mode is only available if a One Condenser or
Two Condenser Head Pressure Module is installed.
Staging Delays
Staging Delays minimum run times and minimum off times are sent
from the VCM-X Modular series controller.
Revised: 12/16/13
(12 pages)
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