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Marvair GAA A/C w/Gas Heat I&O Manual
06/2023 Rev.5
The gas heat and air conditioner has a LED indicator that shows operating status and simplifies service
by flashing fault codes.
On-Steady
Control Operation Normal
1 Flash
Open Air pressure switch, limit switch or flame rollout switch
2 Flashes
Pressure switch stuck closed
3 Flashes
Ignition / flame sensor failure
4 Flashes
Repeated flame loss
5 Flashes
Internal control fault
6 Flashes
Repeated pressure switch losses
LED Flash Code Key
1.6 Ventilation Options
Configuration “C”: Up to 100% Modulating Economizer
The economizer reduces the cost of air conditioning by using outside air when acceptable to cool the
room (Free Cooling). The factory installed Marvair® economizer has integral pressure relief.
Control Board Logic:
Upon a “Call for Cooling”, the economizer control board calculates whether the
HVAC operates in economizer mode or mechanical cooling mode based on outdoor temperature (dry
bulb) or temperature/humidity (enthalpy). When outdoor conditions are favorable for economizer cooling
, the damper drives open and modulates to maintain a 55ºF mixed air temperature through the supply
grille. When outdoor conditions are not favorable for economizer cooling, the economizer damper remains
closed, and the HVAC unit will operate in mechanical cooling mode.
Features Designed for Telecommunication applications:
Hydrogen Fault Input: When 24VAC is applied
to the H_FLT input, the economizer board forces the damper to open 100% for emergency ventilation.
The compressor does not operate during Hydrogen Fault/Emergency Ventilation. Thermostat must provide
the fan “G” signal to HVAC to activate the indoor blower.
Forced Mechanical Cooling:
When 24VAC is applied to the FC input of the economizer board, the
economizer damper is forced closed, and the HVAC will operate in mechanical cooling mode. This is
considered as economizer override in the event economizer cooling is not sufficient for the heat load.
Thermostat must provide the fan “G” signal to HVAC to activate the indoor blower.
Economizer Status:
The economizer board has contacts that when used with the Marvair CommStat 4
Telecom HVAC Controller, change state to provide feedback to the CommStat 4 to indicate when the
HVAC is in economizer mode verses mechanical cooling mode. This feedback allows the CommStat 4
to initiate the forced cooling feature to override economizer cooling and force mechanical cooling.
When used with minimum position potentiometer (optional), the Marvair® economizer can meet require-
ments of ASHRAE Std. 62.
Configuration “D”: Two-Position Motorized Fresh Air Damper w/Pressure Relief Ventilation
Control Board Logic:
The 92589 control board allows the position of the “D” damper to be set for desired
outside air intake from fully closed to fully open. Setting 15 of the control board configuration menu
allows the user to set the position from 20 (2VDC / Closed) to 100 (10VDC 100% open). The damper
position can be adjusted in 1VDC increments to any position from closed to 100% open as required.
Operation:
Anytime the indoor blower operates, the damper drives open to the position selected in the
control board configuration menu setting 15. When the indoor blower stops operation the motorized
damper spring returns to the fully closed position.
Note:
This circuit does not interrupt the compressor or heater operation.
