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Marvair MGA3090-3180 Wall Mount AC I&O Manual 05/2023 Rev.14
10vdc signal from the ECO output of the control board to drive the motorized damper fully open.
Note:
The compressor and electric heat WILL NOT operate while in the emergency ventilation
mode.
7.3 Forced Cooling (economizer equipped systems) –
During economizer cooling, if a request
for “Forced Cooling” (FC-signal via Digital input or Modbus) is present. The control board
will force the economizer to close and start the compressor to operate at full capacity cooling.
This is considered an override of the economizer in the event economizer cooling can’t keep up
with the cooling demand in economizer mode. The Indoor Motor at the “Y2” speed setting on
the board or via Modbus and the system will operate in normal cooling mode until the request
for FC is satisfied. Once satisfied the system will be allowed to return to economizer operation
if conditions are favorable.
7.4 Low Voltage (Brownout) –
The control board monitors the 24 VAC power supply for low voltage
protection. When the power supply voltage is 16 VAC or less for 10 seconds the control board
will de-energize all outputs. This is considered a voltage brownout (low voltage) condition and
the display of the control board will show “03” as an indicator of brownout (low voltage). When
the voltage rises back to 17 VAC, the control board will allow the system to operate.
Note:
The nominal power supply for the control board is 24VAC and this voltage should be
confirmed during startup to assure normal operation.
8.0 Smoke / Fire Shutdown
8.1 System Shutdown Contact Wiring –
Add Normally Closed Dry contacts as shown for immediate
shutdown of HVAC upon contacts opening.
