Johnson Controls
5513350-JTG-1018
77
Fail-Safe Mode
In fail-safe mode, compressor operation maybe limited be-
low a user selected ambient temperature. Condenser fan
operation is controlled by ambient temperature and com-
pressor operation. If the saturated liquid line temperature is
not reliable, one condenser fan is energized for every com-
pressor that energizes, and the variable speed condenser
fan runs at 100%.
When the saturated liquid line temperature becomes reli-
able, the unit reverts to saturated liquid line temperature
control.
Low Ambient Mode
This functionality is only available during saturated liquid
line temperature control.
When low ambient mode is NOT enabled on a circuit, the
lower range of the OAT cooling enable setpoint is 45.0°F.
When low ambient mode IS enabled on a circuit, the lower
range of the OAT cooling enable setpoint is -10.0°F.
Low ambient mode cannot be enabled on a circuit unless
there is a variable speed condenser fan and liquid line
pressure sensor installed on that circuit.
Heating System
The controller supports multiple heating types including
electric heat (staged, modulated), gas heat (staged, modu
-
lated), and a hydronic heating coil. The supported heating-
related features include warm-up, discharge air (DA) tem
-
pering, load shedding, and run time equalization.
Electric Heat
The application supports up to eight stages of electric heat
as well as modulated electric heat.
Staged Electric Heat
If the DAT is lower than the heating setpoint minus the
deadband, stages are energized. If the DAT is greater than
the heating setpoint plus the deadband, the stages are de-
energized.
Modulating Electric Heat
If the DAT is lower than the heating setpoint, the heating
demand increases. If the DAT is greater than the heating
setpoint, the heating demand decreases.
Run Time Equalization
The controller records the number of starts and run time
statistics for each stage of electric heat.
At the initiation of each heating demand, the stage with
the lowest total run time energizes first. When run time is
equal, the staging shall be in numerical order. The stage
with the next lowest total run time energizes next and so
on. At the termination of heating demand, the stages with
the highest run time stage OFF in reverse order. Run time
equalization only applies to equally sized, non-modulating
heating stages.
Gas Heating
The application supports up to six stages in three furnace
modules. The concept behind the staged and modulating fur-
nace options is to offer multiple furnace modules, with each
module being its own self-contained, fully functioning furnace.
Staged Gas Heat
If the DAT is lower than the heating setpoint minus the dead
-
band, the staged heating demand increases. If the DAT is
greater than the heating setpoint plus the deadband, the
staged heating demand decreases. The gas heat modules
are energized in response to the heating demand. Each gas
heat module has a low fire and a high fire mode, which are
individually energized in response to the heating demand.
Low fire is always energized prior to high fire.
Modulating Gas Heat
To accomplish this, one furnace module is adapted for
modulation. The selected furnace module is started and
modulated, while the other ON/OFF furnace modules are
staged, which allows a much broader modulation range.
If the DAT is lower than the heating setpoint, the heating
demand increases. If the DAT is greater than the heating
setpoint, the heating demand decreases. Each gas heat
module has a low fire and a high fire mode, which are indi
-
vidually energized in response to the heating demand. Low
fire is always energized prior to high fire.
Modulating Hydronic Heating Coil
If the DAT is lower than the heating setpoint, the percent
command increases. If the DAT is greater than the heating
setpoint, the percent command decreases. The application
setup of either direct or reverse action allows support for
either normally open or normally closed valves.
Controls (Continued)