33
Operation
6.0 NORMAL SEQUENCE OF OPERATION
The following sections provide details on how the
(-)A15AZ/(-)P16AZ/(-)A16AZ outdoor systems are
designed to operate under normal conditions. Under
abnormal conditions, Active Compressor and Inverter
Protection features built into the controls may alter
how the system operates to protect the compressor
and inverter from damage. The sequence of operation
is based on the system being set up for EcoNet
TM
communications using an EcoNet
TM
enabled air-handler
or gas furnace and an EcoNet
TM
Control Center. A
section is provided at the end that describes how the
system will operate if a conventional 24VAC 2-stage
thermostat is used.
NOTE: The use of a conventional 24VAC thermostat
eliminates many of the advanced operating and
diagnostic features the customer has paid for and
is strongly discouraged.
6.1 Cooling and Heating Mode
The RD17AZ unit has several modes of operation.
These modes are listed and described below.
Installations with Econet Stat and matching Rheem
indoor: The unit will have fully variable operation and
has overdrive capability in both cooling and heating.
Heating mode operation allows the unit to deliver up
to 70% of rated nominal capacity at 5°F. All diagnostic
features of the Econet system are available through the
thermostat and the Contractor App.
Installations with a matching Econet indoor unit, and
a 24V legacy 2 Stage thermostat: The unit will have
3 speeds in both cooling and heating. Cooling and
heating capacities are limited to the nominal rating of
the system. Diagnostic information is available through
the Contractor App. The unit will run on low stage
for a period when a Y1 call is given, and will bump to
intermediate speed and continue to run at that speed
until the call is satisfied, or the thermostat gives a call
for high stage by energizing Y2.
Installations using a 2 Stage non Econet indoor and
a 2 Stage 24V thermostat: The unit will operate at 2
discreet speeds in both cooling and heating. Capacity
is limited to the nominal rated capacity in heating and
cooling modes. Diagnostic data is available through
the Contractor App.
Installations that use an existing indoor coil with a
24V (Y1 Only) thermostat and have the utility terminals
shorted on the UODC board will start the unit when
there is a 24V call from the thermostat. The UODC
will vary the outdoor unit speed, compressor and
fan, to maintain the needed capacity based on the
temperature of the gas returning from the indoor unit.
With the indoor modified to provide 2 stages of airflow,
the unit will adjust capacity to deliver the proper cooling
and heating for the space. A Y2 wire is not required to
be run to the outdoor unit from the 2 stage stat.
Note: Anytime the compressor goes to line
operation, the unit shall stay there until the heating/
cooling satisfies the thermostat demand
6.2 On-Demand Cooling
Dehumidication
The EcoNet
TM
Control Center can be configured for
On-Demand Dehumidification. This feature allows
the system to automatically increase the level of
dehumidification in the cooling mode by decreasing the
indoor air-flow by 15% when the indoor relative humidity
measured at the Control Center rises above the set-
point. Once the relative humidity drops to or below the
set-point, the indoor air-flow level returns to normal.
6.3 Low Ambient Cooling Mode
In some installations, a requirement exists for cooling
a controlled air space when the outdoor ambient is
below the normal range for cooling such as a computer
room or other enclosed areas where a large heat load
exists that must be kept cool. Low ambient cooling is
a special cooling mode that allows the unit to provide
cooling when the outdoor temperature is below low
ambient temperature. When necessary, the outdoor
fan shall be cycled off to maintain liquid pressure in
the system. Operation below low ambient temperature
requires special interpretation of the state of the suction
pressure. If the outdoor air temperature is less than the
low ambient temperature, a flag shall be set and the
low ambient cooling algorithm shall run. If the outdoor
temperature rises one degree above the low ambient
temperature, the low ambient cooling algorithm shall
turn off and the flag shall be reset
Note: This mode shall not be active if any sensor
error code is active.
6.4 Supplemental Electric
Heat in
Heating Mode
If the building load should exceed the heating capacity
in extreme outdoor conditions, the EcoNet
TM
Control
Center or 24 VAC 2-stage thermostat will direct the
RH3VZ or RHMVZ air-handler to energize supplemental
electric heat as required to meet the building load. The
indoor air-flow will be forced to operate at the maximum
level for the system. For 13kW heaters and higher, the
supplemental electric heat will be energized in two
stages as required. The compressor and outdoor fan
will continue to operate at maximum capacity while
supplemental electric heat is energized.
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