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Marvair Wall Mount Heat Pump I&O Manual
11/2021 New
and temperature. Next it is pumped to the indoor coil where the heat will be released into the room. The
compressed refrigerant vapor will condense to its liquid state as it gives up heat. Finally, liquid flows
through a metering device into the evaporator where the cycle will be repeated.
Optional electric strip heat is available for all models. Please see Appendix A for instructions on field
installation of electric heat.
Options for Outside Air for Ventilation
ASHRAE standard 62 requires 15 cfm of outside air per occupant of a classroom. To meet this requirement,
Marvair offers seven ventilation packages for every budget and requirement.
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
requirements of ASHRAE Std. 62.
Configuration “D”: Two-Position Motorized Fresh Air Damper w/Pressure Relief Ventilation
Factory Installed Relay Logic: Upon a “Call for indoor blower” via a 24V signal (G), the motorized damper
opens to a maximum of 50% of the fully open position. The open position can be decreased from 50%
by adjusting the rod position on the drive linkage. In this case, the damper will not open unless there’s
a call for the indoor blower.
Note:
This circuit does not interrupt the compressor or heater operation.
Configuration “E”: Two-Position Motorized Fresh Air Damper w/Pressure Relief Ventilation &
Independent Control
Factory Installed Relay Logic: Upon a “Call for Motorized damper” via a 24V signal from an external
user-installed device, the motorized damper opens to a maximum of 50% of the fully open position. The
open position can be decreased from 50% by adjusting the rod position on the drive linkage.
