10
Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
05/2023 Rev.21
In applications where a shelter has redundant air conditioning units and is controlled by a lead lag control-
ler (CommStat Touch, CommStat 4, CommStat 3 HVAC Controller), most times the dehumidification
option is only necessary on one of the two units. It is possible for one unit to be operating in the cooling
mode while the unit with dehumidification is operating at the same time. If the cooling unit does not
maintain the shelter temperature set point, the unit with dehumidification will go into the cooling mode.
It does not matter whether the unit with dehumidification is the lead or lag unit.
Three Phase Voltage Monitor
Continuously measures the voltage of each of the three phases. The monitor separately senses low
and high voltage, voltage unbalance including phase loss and phase reversal. An LED indicator glows
when all voltages are acceptable. Automatically resets when voltages and phases are within operating
tolerances. Not required on 1ø units.
Dirty Filter Indicator
A diaphragm type of indicator measures the air pressure on either side of the filter and when the pressure
drops below the set point, a red LED is illuminated. The set point is adjustable.
Protective Coil Coatings
Either the condenser or evaporator coil can be coated, however, coating of the evaporator coil is not
common. For harsh conditions, e.g., power plants, paper mills or sites were the unit will be exposed to
salt water, the condenser coil should be coated. Note: Cooling capacity may be reduced by up to 5%
on units with coated coils.
Thermal Expansion Valve
Available on all Marvair air conditioners. Improves performance in hot ambient temperatures.
High Filtration
Selected units are built with larger blowers/motors for use with higher efficiency filters with MERV
ratings of 11, 13 and 14 when tested to ASHRAE 52.2. Units with economizers have a pre-filter on the
outside air.
Lockable Disconnect Access Cover Plate
The access plate to the service disconnect switch can be equipped with a lockable cover.
Cold Climate Kit
Controls and components which allow the units to operate in extremely cold temperatures. The kit
includes a suction line accumulator, thermal expansion valve (TXV), crankcase heater, hard start kit,
and an outdoor thermostat and fan cycle switch. The fan cycle control is standard on all Marvair air
conditioners and operates based upon the liquid line pressure. The outside thermostat opens whenever
the outside temperature is below 50°F (10°C) and closes when the outside temperature is 50°F (10°C)
or higher. Whenever the temperature is below 50°F (10°C), the fan cycle switch is in the circuit; when
temperatures are 50°F (10°C) or higher, the fan cycle switch is not in the circuit. The outdoor thermostat
is used with a TXV to prevent excessive cycling or “hunting” of the TXV.
Desert Duty
The Desert Duty package is a factory installed package of components and cabinet modifications which
permit operation in harsh environments. To prevent sand and dust infiltration, the electrical control
box is sealed. A closed loop design on non-economizer units insures that no outside air is introduced
into the shelter. Note: Units with an economizer may be ordered with the Desert Duty Package. If the
air conditioner is required with the Desert Duty Package, sand intrusion into the shelter should be
considered. Units without an economizer will operate from 20°F to 131°F (-7°C to 55°C). Economizer
equipped units will operate from -40°F to 131°F (-29°C to 55°C).
