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Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
05/2023 Rev.21
to the “Y1” speed setting on the board or via Modbus. It also outputs a request dependent
(based on FCC IN) control signal for the Outdoor Fan Motor (Only applicable to ECM
motors). In Stage 1 Cooling operation, the compressor operates at partial capacity and the
indoor fan remains on continuously but the outdoor fan modulates based on liquid line
temperature. The Fan Cycle Control Sensor (Low Ambient Control Sensor) monitors the
liquid line to maintain a 90F liquid line temperature. When the liquid line temperature is
below 80F the outdoor fan will shut off. A liquid line temperature above 115F will force
the outdoor fan to operate at the maximum speed set on the control board for setting
7 in the configuration menu. The outdoor fan will speed up and slow down between
liquid line temperature of 80F and 115F. Systems with (PSC Outdoor Motors) utilizes a
Fan Cycle Switch which closes at 400 PSIG to energize the OFR (outdoor fan relay) to
start the outdoor fan which runs until the switch reopens (at 290 PSIG). These outputs
function as described until the Cooling setpoint is satisfied. This is considered as ON/
OFF fan cycle control and the PSC motor will not modulate.
Note:
Single Stage compressors operate at full capacity upon a request for Y1.
2.2.2 Y1 + Y2 + O Cooling (Full Capacity 2nd Stage) –
If the space temperature continues
to increase pass the defined differential, Stage 2 Cooling (Y1+Y2+O input) is energized.
Under normal operation, this energizes the Compressor 2 Output (CC2). The Indoor Fan
motor, will operate at “Y2” speed instead of “Y1” speed since Y2 has higher priority.
These outputs remain energized until the cooling setpoint is satisfied. Once the setpoint
is satisfied, the Compressor and the Outdoor fan outputs are de-energized. The Indoor
motor continues to run based on the fan purge timer setpoint (default 90 seconds) selected
in setting 3 of the configuration menu of the control board.
Note:
2 Stage compressors require a request for Y2 to operate at full capacity in Cooling
operation. All Air-conditioners and Heat Pump systems with 2 stage compressors are
allowed 2 stage cooling operation.
Note:
With staged compressors, a CC2 output without a CC1 output will neither result
in partial capacity nor full capacity. Only CC1 output can achieve partial capacity. Both
CC1 and CC2 outputs are required to achieve full capacity.
3.0 Economizer Operation (If Equipped)
Damper Actuator
The damper actuator is a 24V motor that modulates the position of the damper blade. It is capable
of driving a full 90 degrees within 90 seconds. The assembly has a spring return to close the
damper during power outage.
3.1 Enthalpy Sensor and Operation –
The enthalpy sensor responds to the total heat content of
the outdoor air to provide the changeover to outside air for free cooling. The control board must
be configured for proper operation of the economizer by selecting Y= Yes in the configuration
menu setting 12. The sensor type must be selected in setting 13 for EN=Enthalpy. The desired
changeover setpoint must be selected in setting 14 (default D=63F@50% rh). Example of
Enthalpy Sensor and Enthalpy curve is shown below.
Note:
Selecting N=No in configuration setting 12 will disable economizer operation.
DANGER
Sever hazard. The economizer contains moving parts capable of causing serious
injury or death. Disconnect power before removing the covering panel.
