Marvair 8AA1024A-1060A & 8AA2036A-2060A I&O Manual
05/2023 Rev.3
25
2.1 Mechanical Cooling (AC systems) –
This section will describe the sequence of operation which
takes place during Direct Expansion (DX) cooling from a control standpoint.
Note:
The system type must be configured for “AC” operation in setting 1 of the configuration
menu of the control board for proper AC system operation. This system type is selected at the
factory and there’s no need to change this setting.
2.1.1 Y1 Cooling (Partial Capacity 1st Stage) –
In normal operating mode, a request for
“Stage1 Cooling” Y1-signal via Digital input or Modbus), energizes Compressor 1 Relay
Output (CC1) on the PCB. The controller provides a continuous control signal associated
to the Indoor Fan Motor, that is proportional 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.
2.1.2 Y1 and Y2 Cooling (Full Capacity 2nd Stage) –
If the space temperature continues to
increase pass the defined differential, Stage 2 Cooling (Y2-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.
2.2 Mechanical Cooling (HP systems) –
This section will describe the sequence of operation which
takes place during Direct Expansion (DX) cooling from a control standpoint. The reversing
valve (O Input) must be energized for Cooling operation on Heat Pump systems.
Note:
The system type must be configured for “HP” operation in setting 1 of the configuration
menu of the control board for proper HP system operation. This system type is selected at the
factory and there’s no need to change this setting.
2.2.1 Y1+ O Cooling (Partial Capacity 1st Stage) –
In normal operating mode, a request for
“Stage1 Cooling” Y1 + O signal via Digital input or Modbus), energizes the Reversing
Valve Output (RV) and Compressor 1 Relay Output (CC1) on the PCB. The controller
provides a continuous control signal associated to the Indoor Fan Motor, that is proportional
