Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
09/2021 Rev.15
9
pressure. The outside thermostat closes whenever the outside temperature is below 50°F (10°C) and
opens 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 fan cycle control is used with a TXV to prevent excessive
cycling or "hunting" of the TXV.
Protective Coating Packages
Typically only the non-economizer units are used in corrosive environments, but the air conditioners
with an economizer is also available with corrosion protection. Two corrosion protection packages are
offered- one for the condenser section (the Coastal Environmental package) and the other for the entire
unit (the Coat-All Package).
The Coastal Environmental Package includes:
• Corrosion resistant fasteners
• Sealed or partially sealed condenser fan motor
• Protective coating applied to all exposed internal copper and metal in the condenser section
• Protective coating on the condenser coil (Luvata Insitu®) contains ES2 (embedded stainless steel
pigment) technology.
The Coat all Package includes all of the above, plus:
• Protective coating on the evaporator coil (Luvata Insitu®) contains ES2 (embedded stainless steel
pigment) technology
• Protective coating on exterior and interior components and sheet metal. (Note: the internal sheet
metal which is insulated, bottom outside panel, and the internal control box are not coated)
Hot Gas Bypass (Non-Economizer Models Only)
Used in specialty applications; i.e., Magnetic Resonance Imaging (MRI) buildings, to prevent magnetic
voltage disturbance caused by compressor cycling. Two hot gas bypass option packages are available
to allow operation to 20°F (-7°C) or minus 20°F (-29°C). Please refer to Hot Gas Bypass Application
Bulletin for details.
Electric Reheat Dehumidification
A humidity controller allows electric heat and cooling to operate simultaneously. Marvair
®
air conditioners
equipped with the dehumidification option allow the indoor humidity of the controlled environment
to be maintained at or below a certain humidity set point. These units do not have the ability to add
humidity to the building.
IMPORTANT
The electrical wire and breaker or fuses must be sized for simultaneous operation
of the electric heater and the air conditioner. Refer to the data sticker on the unit or
the appropriate Air Conditioner Product Data Sheet for the sizing information.
Dehumidification is achieved by operating mechanical cooling in conjunction with electric reheat. The
strip heat is sized approximately to the sensible capacity of the total tonnage of the machine (i.e., on a
24,000 BTU unit the strip heat is sized at approximately 20,000 BTU). Because the strip heat is sized
to the approximate sensible cooling capacity, only selected models are available.
Operation:
When the humidity rises above the set point on the humidity controller both mechanical cooling and
electric reheat operate to temper the air and lower the humidity. If the temperature in the controlled
environment rises above the set point of the thermostat and the unit is operating in the dehumidification
mode, the call for cooling will override the call for dehumidification and the strip heat is disengaged
until the thermostat is satisfied. This assures the environment temperature is maintained as first priority
and humidity control is second.
