Marvair MAA1018A User manual

MODELS:
MAA1018A-MAA1060A, MGA1072A
(Single Stage)
MAA2060A-MAA2072A, MGA2072A
(2-Stage)
Installation & Operation Manual
10 & 11 EER Vertical Wall-Mount Air Conditioners
Manufactured By:
Marvair, An AirX Climate Solutions Brand
P.O. Box 400 • Cordele, Georgia 31010 • 156 Seedling Drive • Cordele, Georgia 31015
[phone] • Fax [phone]
E-mail: [e-mail] • Internet: www.Marvair.com
The most current version of this manual can be found at www.Marvair.com.
IMPORTANT
This manual may include information for options and features which may not be
included on the unit being installed. Refer to the unit data label or Model Identication
to determine which features and options this unit is equipped with.
INSTALLER: Afx the instructions on the inside of the building adjacent to the thermostat.
END USER: Retain this manual for future reference.
Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
12/2021 Rev.16
Air Conditioner Product Manual
Vertical Wall-Mount Air Conditioners
with Front Control Box Panel

2
Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
12/2021 Rev.16
How To Use This Manual
This manual is intended to be a guide to the Marvair Wall Mount family of vertical air conditioners. It contains installation,
troubleshooting, maintenance, warranty, and application information. The information contained in this manual is to be
used by the installer as a guide only. This manual does not supersede or circumvent any applicable national or local codes.
If you are installing the Marvair unit, rst read Chapter 1 and scan the entire manual before beginning the installation as
described in Chapter 2. Chapter 1 contains general, descriptive information and provides an overview which can speed
up the installation process and simplify troubleshooting.
If a malfunction occurs, follow this troubleshooting sequence:
1. Make sure you understand how the Marvair unit works (Chapters 1 & 3).
2. Identify and correct installation errors (Chapter 2).
3. Refer to the troubleshooting information in Chapter 4.
If you are still unable to correct the problem, contact the Factory at 1-800-841-7854 for additional assistance.
Please read the following “Important Safety Precautions” before beginning any work.
Important Safety Precautions
1. USE CARE when LIFTING or TRANSPORTING equipment.
2. TRANSPORT the UNIT UPRIGHT. Laying it down on its side may cause oil to leave the compressor and breakage
or damage to other components.
3. TURN ELECTRICAL POWER OFF AT THE breaker or fuse box BEFORE installing or working on the equipment.
LINE VOLTAGES ARE HAZARDOUS or LETHAL.
4. OBSERVE and COMPLY with ALL applicable PLUMBING, ELECTRICAL, and BUILDING CODES and ordinances.
5. SERVICE may be performed ONLY by QUALIFIED and EXPERIENCED PERSONS.
* Wear safety goggles when servicing the refrigeration circuit
* Beware of hot surfaces on refrigerant circuit components
* Beware of sharp edges on sheet metal components
* Use care when recovering or adding refrigerant
6. Use COMMON SENSE - BE SAFETY-CONSCIOUS
This is the safety alert symbol . When you see this symbol on the Marvair unit and in the instruction manuals
be alert to the potential for personal injury. Understand the signal word DANGER, WARNING, CAUTION and
IMPORTANT. These words are used to identify levels of the seriousness of the hazard.
DANGER Failure to comply will result in death or severe personal injury and/or property damage.
WARNING Failure to comply could result in death or severe personal injury and/or property damage.
CAUTION Failure to comply could result in minor personal injury and/or property damage.
IMPORTANT Used to point out helpful suggestions that will result in improved installation, reliability or
operation.
© 12/2021 Marvair, An AirX Climate Solutions Brand
AS PART OF THE MARVAIR CONTINUOUS IMPROVEMENT PROGRAM, SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE.

Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
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3
WARNING
• If the information in these instructions are not followed exactly, a re may result causing
property damage, personal injury or loss of life.
• Read all instructions carefully prior to beginning the installation. Do not begin
installation if you do not understand any of the instructions.
• Improper installation, adjustment, alteration, service or maintenance can cause property
damage, personal injury or loss of life.
• Installation and service must be performed by a qualied installer or service agency in
accordance with these instructions and in compliance with all codes and requirements
of authorities having jurisdiction.
INSTALLER: Afx the instructions on the inside of the building adjacent to the
thermostat.
END USER: Retain these instructions for future reference.
Table of Contents
Chapter 1 Marvair Wall Mount Air Conditioner Description & Specications
1.1 General Description .................................................................................................................................5
1.2 Model Identication .................................................................................................................................6
1.3 Serial Number Date Code ........................................................................................................................7
1.4 Air Flow, Weights and Filter Sizes...........................................................................................................7
1.5 General Operation ....................................................................................................................................7
1.6 Optional Controls and Packages ..............................................................................................................8
1.7 Electrical Operation ...............................................................................................................................11
1.8 Economizer Components .......................................................................................................................17
Chapter 2 Electronic Control Board
2.1 Introduction ............................................................................................................................................21
2.2 Installation and Replacement .................................................................................................................22
2.3 Operation................................................................................................................................................22
2.4 Sequence of Operation ...........................................................................................................................26
Chapter 3 Installation
3.1 Equipment Inspection.............................................................................................................................32
3.2 Installation Requirements.......................................................................................................................32
3.3 Installation Materials .............................................................................................................................34
3.4 Porting and Duct Work ..........................................................................................................................35
3.5 Fresh Air Hood Installation ...................................................................................................................36
3.6 Bracket Installation ...............................................................................................................................37
3.7 Mounting the Unit .................................................................................................................................37
3.8 Electrical Connections ...........................................................................................................................38
Chapter 4 Start-Up
4.1 Check-Out of Cooling Cycle .................................................................................................................42
4.2 Check-Out of Heating Cycle..................................................................................................................42

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Chapter 5 Troubleshooting
5.1 Overview ................................................................................................................................................43
5.2 Failure Symptoms Guide........................................................................................................................44
5.3 Compressor Troubleshooting .................................................................................................................44
5.4 Control Board Diagnosis........................................................................................................................45
Chapter 6 Maintenance
6.1 Scheduled Maintenance .........................................................................................................................46
Chapter 7 Warranty
7.1 Marvair Limited Product Warranty ........................................................................................................47
Chapter 8 Start-Up Checklist
8.1 Start-Up & Commissioning Form..........................................................................................................48
Appendix A
Installation Instructions for Field Installed Electric Heaters ...........................................................................52
Illustrations
Figure 1a. Typical Electrical Schematic - Model MAA..............................................................................12
Figure 1b. Typical Electrical Schematic - Model MAA..............................................................................13
Figure 1c. Typical Electrical Schematic - Model MAA (Alternate Construction).....................................14
Figure 1d. Typical Electrical Schematic - Model MAA (Alternate Construction)......................................15
Figure 1e. Typical Electrical Schematic - Model MAA (Alternate Construction)......................................16
Figure 2. Dry Bulb sensor..........................................................................................................................18
Figure 3. Enthalpy Sensor Temperature Control Points ............................................................................19
Figure 4. Electrical Controls, HVESA Alternate Construction .................................................................19
Figure 5. Economizer Control Board ........................................................................................................20
Figure 6a. Setting the Speed for the Y1 and Y2 Operation for Indoor Motor ............................................23
Figure 6b. Second Stage Cooling Speed .....................................................................................................23
Figure 7. Output Termination for Indoor Motor Control Signal ...............................................................24
Figure 8. Outdoor Motor Speed Setting ....................................................................................................24
Figure 9. Output Termination for Outdoor Motor Control Signal.............................................................24
Figure 10. Communications SetUp .............................................................................................................25
Figure 11. Fresh Air Hood Damper, Models 1024-1072.............................................................................36
Figure 12. Wall Mounting Detail.................................................................................................................37
Figure 13a. Humidistat Wiring Details..........................................................................................................40
Figure 13b. Thermostat Connection Diagram ...............................................................................................40
Figure 13c. CommStat™ 3 HVAC Controller Wiring Detail........................................................................41
Figure 13d. CommStat™ 4 HVAC Controller Wiring Detail........................................................................41
Tables
Table 1 CFM @ External Static Pressure .................................................................................................7
Table 2 Return Air Filter Sizes .................................................................................................................7
Table 3 Installed Unit Weights..................................................................................................................7
Table 4 Ambient Temperature Operating Range ......................................................................................7
Table 5 Refrigerant Charge.......................................................................................................................8
Table 6. MODBUS Network Address DIP Switch Positions ..................................................................26
Table 7a. MODBUS Discrete Registers ....................................................................................................30
Table 7b. MODBUS Registers...................................................................................................................31
Table 8 Minimum Clearances.................................................................................................................33
Table 9 Voltage Limitations....................................................................................................................33
Table 10 Maximum Static Pressure ..........................................................................................................36

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Chapter 1 Description & Specications
1.1 General Description
The Marvair MAA and MGA are a series of vertical wall-mounted air conditioning systems that provide
heating, cooling, and ventilation for electronic equipment shelters, process control centers, and other
applications with high internal heat gains. The series includes multiple sizes and nominal cooling
capacities from 18,000 to 72,000 BTUH. Resistance heating elements are available in various wattages.
MAA modes are available with cooling capacities of 18,000 to 60,000 BTUH and EER’s of 11.00 to
11.50. MGA models have 72,000 BTUH (6 ton) capacity and are 10 EER. The Marvair Product Data
Sheets have detailed information on the capacities and efciencies for each model.
See Appendix A for instructions on eld installation of electric heat.
Marvair air conditioners feature an exclusive electronic control board. The control board consolidates
several of the electrical components and improves the air conditioner’s reliability. The control board
replaces the blower relay, the lockout relay, the compressor time delay and the timed low pressure
bypass. In addition, the control board has LED’s to indicate operating status and fault conditions to
assist the service technician. A complete description of functions of the control board is in Chapter 2.
All models are designed for easy installation and service. Major components are accessible for service
beneath external panels.
All units have internal disconnects (optional on 380V and 575V). Follow local codes for external
disconnect requirements.
Marvair wall mount air conditioners have a 0-15% manual outside air damper as standard equipment.
All models are available with an optional factory installed economizer for 100% free cooling with
outside air.

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1.2 Model Identication
The model identication number is found on the data sticker. Rating plate located on side panel.
Example M A A 1 0 3 6 A D 0 5 0 C + + + + 1 E A + A 2 1 + + + + + +
Position 1234567891011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
1Unit Designation/Family M = Marvair Wall Mount
2Energy Efciency Ratio
(EER)
A = 11
G = 10
3Refrigerant Type A = R-410a
4Compressor Type/Quantity 1 = Fixed Speed/Single
2 = 2-Stage/Single
5
Unit Capacity/Nominal
Cooling (BTUH)
018 = 18,000 042 = 42,000
020 = 20,000 048 = 48,000
024 = 24,000 060 = 60,000
030 = 30,000 072 = 72,000
036 = 36,000
6
7
8System Type A = Air Conditioner
9Power Supply
(Volts-Hz-Phase)
A= 208/230-60-1 D= 460-60-3
C= 208/230-60-3 Z= 575-60-3
10
Heat Designation
@ Rated Voltage
000 = No Heat 080 = 8KW
022 = 2.2KW 090 = 9KW
036 = 3.6KW 100 = 10KW
040 = 4KW 120 = 12KW
050 = 5KW 150 = 15KW
060 = 6KW
11
12
13 Ventilation
Conguration
A = Solid Front Door
C = Economizer
D = Motorized Damper w/Pressure Relief
E = Motorized Damper w/Pressure Relief &
Independent Motorized Damper Control
F = No Free Cooling, 100% Emergency
Ventilation Only w/Independent Control
N = Barometric Damper w/15% OSA
Y = Manual Damper w/No Pressure Relief
Z = Manual Damper w/Pressure Relief
+ = None
$ = Special
14 Dehumidication
G = Hot Gas Reheat
R = Electric Reheat
T = Electric Reheat w/Humidity Control
+ = None
$ = Special
15 Controls
A = Power Fail Alarm w/Additional Lockouts
C = 24V EMS Relay Kit
D = 24V EMS Relay Kit w/Factory
Installed T-Stat
E = Factory Installed T-Stat
+ = None
$ = Special
16 Operating Condition
A = Evaporator Freeze Sensor (EFS)
C = EFS w/Hot Gas Bypass
D = Desert Duty
E = Extreme Duty
F = Desert Duty w/Hard Start
G = Desert Duty w/EFS
H = Desert Duty w/Hard Start & EFS
J = Extreme Duty w/Hard Start
K = Extreme Duty w/EFS
M = Extreme Duty w/Hard Start & EFS
N = Hard Start
P = Hard Start w/Low Ambient & CCH
Q = Hard Start w/Low Ambient &
Fan Cycle Control (FCC)
R = Crank Case Heater (CCH)
T = Hard Start w/EFS
U = Hard Start w/Hot Gas Bypass
V = Hard Start w/Low Ambient & CCH & EFS
W = Low Ambient w/CCH
X = Hot Gas Bypass
Y = Low Ambient w/CCH & FCC
Z = Low Ambient w/CCH & EFS
1 = Low Ambient w/FCC
2 = Low Ambient w/FCC & EFS
3 = CCH w/Hot Gas Bypass
+ = None
$ = Special
17 Indoor Air Quality Features
D = Dry Bulb Sensor
E = Dry Bulb Sensor w/Dirty Filter
G = Dirty Filter Sensor
+ = None
$ = Special
18 Air Flow
1 = Top Supply/Bottom Return
2 = Center Supply (Reverse)
3 = Bottom Supply/Top Return (Counter)
4 = Top Panel Discharge
5 = Centrifugal Blowers
6 = 3T3
7 = 3T5
8 = 4T2
9 = 4T3
A = 3T2
$ = Special
19 Compressor Location
C= Center - All 6 ton units and above
D= Left Hand - All 31/2 to 5 ton units
E= Right Hand - All 11/2 to 3 ton units
20 Filter Option
A = 2” Pleated (MERV 8, AC/HP-C)
C = 2” Charcoal
D = MERV 11 High Filtration Package
E = MERV 13 High Filtration Package
F = Filter Access Through Return Air Grille
W = Aluminum Washable
+ = None
$ = Special
21 Corrosion Protection
A = Condenser Coil Only
C = Evaporator Coil Only
D = Both Coils Condenser & Evaporator
E = All Coils Cond/Evap/Reheat
F = Coat All
G = Coastal Package & Evaporator Coil
K = Coastal Package
+ = None
$ = Special
22 Engineering Revision
Level
A1
A2
B2
23
24 Cabinet Color
1 = Marvair Beige
2 = Gray
3 = Carlsbad Canyon
4 = White
5 = Stainless Steel Exterior
6 = Dark Bronze
7 = .050 Aluminum Stucco
8 = Mesa Tan
9 = Pebble Gray
A = Stainless Steel - Unit
$ = Custom Color (Powder Coat)
25 Sound Attenuation 2 = Compressor Blanket
+ = None
26 Security Option
A = Lockable Access Plate/Tamper Proof
C = Tamper Proof Screws
D = Lockable Access Plate w/Tamper Proof
+ = None
$ = Special
27 Fastener/Drain Pan Option
A = Stainless Steel Fasteners
C = Stainless Steel Drain Pan
D = Stainless Steel Fasteners & Drain Pan
+ = None
$ = Special
28 Unused + = None
$ = Special
29 Unused + = None
$ = Special
30 Special Variation
+ = None
$ = Special Conguration Not Covered by
Model Nomenclature
Note: Not all options are available with all congurations. Contact your Marvair sales representative for
conguration details and feature compatibility.

Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
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1.3 Serial Number Date Code
20 = 2020 01 = January 05 = May 09 = September
21 = 2021 02 = February 06 = June 10= October
22 = 2022 03= March 07 = July 11 = November
23 = 2023 04 = April 08 = August 12 = December
1.4 Air Flow, Weights and Filter Sizes
Complete electrical and performance specications and dimensional drawings are in the Marvair Wall
Mount Air Conditioner Product Data Sheets.
Note: Follow local codes and standards when designing duct runs to deliver the required airow.
Minimize noise and excessive pressure drops caused by duct aspect ratio changes, bends, dampers and
outlet grilles in duct runs.
Model 0.10 0.15 0.20 0.25 0.30 0.40 0.50
MAA1018 685 670 670 642 640 600
MAA1020 800 785 770 725 680 600
MAA1024 800 785 770 725 680 600 500
MAA1030 1200 1150 1100 1050 1000 900 800
MAA1036 1290 1230 1170 1115 1060 1000 920
MAA1042 1500 1430 1360 1295 1230 1160 1070
MAA1048 1950 1900 1850 1815 1760 1680 1590
MAA1060/MAA2072 & MGA1072 1900 1850 1800 1700 1600 1500 1350
Values in bold are the minimum air flow.
Air flow ratings of 208-230 volt units are at 230v. Air flow ratings of 460 volt units are at 460 volts. Operation of units at a voltage different from the
rating point will affect air flow.
Table 1. CFM @ External Static Pressure (Wet Coil) (IWG)
Model INCHES MILLIMETERS PART NUMBER FILTERS PER UNIT MERV RATING
MAA1018 14 x 12 1 356 x 305 x 25 P/80122 1N/A
MAA1020/1024 16 x 25 x 2 406 x 635 x 51 80137 1 8
MAA1024/1030/1036 "B2" INTERNAL 16 x 30 x 1 406 x 762 x 25 80136 1 N/A
MAA1024 "B2" RETURN GRILLE 11½ x 19½ x 1 292 x 495 x 25 91983 1 N/A
MAA1030/1036 & MAA2072 18 x 30 x 2 457 x 762 x 51 93184 1 8
MAA1030/1036 "B2" RETURN GRILLE 27½ x 13½ x 1 699 x 343 x 25 80769 1 N/A
MAA1042/1048 36½ x 22 x 2 927 x 559 x 51 80162 1 8
MAA1060 18 x 24 x 2 457 x 610 x 51 81257 2 8
MGA1072 18 x 24 x 2 457 x 610 x 51 81257 2 8
Table 2. Return Air Filter Sizes
Model Weight Base w/Economizer w/3 Phase w/Economizer & 3 Phase
MAA1018 Pounds (Kilograms) 265 (120) N/A N/A N/A
MAA1020/MAA1024 Pounds (Kilograms) 337 (153) 357 (162) 356 (161) 376 (171)
MAA1024/1030 "B2" Pounds (Kilograms) 378 (171) 400 (181) 397 (180) 419 (190)
MAA1030/MAA1036 Pounds (Kilograms) 397 (180) 419 (190) 416 (189) 438 (199)
MAA1036 "B2" Pounds (Kilograms) 380 (172) 403 (183) 418 (190) 441 (200)
MAA1042/MAA1048 Pounds (Kilograms) 453 (205) 476 (216) 491 (223) 514 (233)
MAA1060 Pounds (Kilograms) 469 (213) 492 (223) 522 (237) 545 (247)
MAA2072 Pounds (Kilograms) 717 (325) 740 (336) 770 (349) 793 (360)
MGA1072 Pounds (Kilograms) 571 (259) 594 (269) 624 (283) 647 (293)
Table 3. Installed Weights for Marvair Wall Mount AC Units
1.5 General Operation
Model Ventilation Conguration Temperature Range
Non-Economizer
Standard ("N") 20ºF – 131ºF (-7ºC – 55ºC)
Desert Duty ("ND") 20ºF – 131ºF (-0ºC – 55ºC)
Extreme Duty ("NE"), 60 Hz Only 0ºF – 131ºF (-18ºC – 55ºC)
With Economizer
Standard ("CE") -40ºF – 131ºF (-40ºC – 55ºC)
Desert Duty ("CD") -40ºF – 131ºF (-40ºC – 55ºC)
Extreme Duty ("CE"), 60 Hz Only -40ºF – 131ºF (-40ºC – 55ºC)
Table 4. Ambient Temperature Operating Range

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Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
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Model MAA1018A MAA1020A MAA1024A MAA1024-1030A
"B2" MAA1030A MAA1036A & "B2" MAA1042AMAA1048A MAA1060A MAA2072A MGA1072A
A A A C D Z A A C D Z A C D Z A C D Z A C D Z A C D Z A C D A C D Z
w/o Hot
Gas Reheat 65 85 85 110 90 105 123 128 125 228 150 160
w/Hot Gas
Reheat N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Table 5. Refrigerant Charge (R410A, Ounces)
Refrigerant Cycle (Cooling Mode)
Marvair air conditioners use R-410A refrigerant in a conventional vapor-compression refrigeration cycle
to transfer heat from air in an enclosed space to the outside. A double blower assembly blows indoor
air across the evaporator. Cold liquid refrigerant passing through the evaporator is boiled into gas by
heat removed from the air. The warmed refrigerant gas enters the compressor where its temperature and
pressure are increased. The hot refrigerant gas condenses to liquid as heat is transferred to outdoor air
drawn across the condenser by the condenser fan. Liquid refrigerant is metered into the evaporator to
repeat the cycle.
Heating Mode
A wall-mounted thermostat controls the heating cycle of models which incorporate resistance heating ele-
ments. On a call for heat, the thermostat closes the heat relay to energize the indoor fan and the resistance
elements. Except on units with the optional dehumidication kit, the compressor is locked out during the
heating cycle. Please see Appendix A for instructions on eld installing electric heaters.
Economizer Operation
The economizer is a regulated damper system with controls. The damper regulates the circulation of outside
air into the enclosure (when the outdoor air conditions are suitable) to reduce the need for mechanical
cooling, save energy, and extend compressor life.
Depending upon the options selected, the damper responds to the enthalpy of the outdoor air. On a call
for cooling from a space thermostat, it operates as follows:
When the enthalpy of the outdoor air is below the set point, the outdoor air damper is proportionally open
(and return air damper is proportionally closed) to maintain between 50°F and 56°F (10°C to 13°C) at
the mixed/discharge air sensor. Integral pressure relief allows the indoor air to exit the shelter through
the air conditioner.
When the enthalpy of the outdoor air is above the set point, the outdoor air damper closes to its minimum
position. A call for cooling from the space thermostat brings on mechanical cooling.
A built-in adjustable minimum position potentiometer controls the amount of outdoor air admitted to
meet minimum ventilation requirements.
1.6 Optional Controls & Packages
Hard Start Kit
Used on single phase equipment to give the compressor higher starting torque under low voltage conditions.
Generally not recommended on units with scroll compressors.
Extreme Duty Package
The Extreme Duty Package allows selected Marvair air conditioners to operate in extremely cold and hot
ambient conditions. The Extreme Duty Kit is always factory installed. Non-economizer air conditioners
will operate from 0° F to 131° F (-18° to 55°C). Economizer equipped air conditioners will operate from
-40° F to 131° F (-40° to 55°C).
The Extreme Duty Package includes a suction line accumulator, thermal expansion valve (TXV), crankcase
heater, hard start kit, an auto reset, high pressure switch 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

Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
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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 Dehumidication
A humidity controller allows electric heat and cooling to operate simultaneously. Marvair®air conditioners
equipped with the dehumidication 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.
Dehumidication 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 dehumidication
mode, the call for cooling will override the call for dehumidication and the strip heat is disengaged
until the thermostat is satised. This assures the environment temperature is maintained as rst priority
and humidity control is second.

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Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
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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 dehumidication
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 dehumidication is operating at the same time. If the cooling unit does not
maintain the shelter temperature set point, the unit with dehumidication will go into the cooling mode.
It does not matter whether the unit with dehumidication 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 lter 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 efciency lters with MERV
ratings of 11, 13 and 14 when tested to ASHRAE 52.2. Units with economizers have a pre-lter 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 modications which
permit operation in harsh environments. To prevent sand and dust inltration, 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).

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Cabinet Color and Material
Marvair air conditioners are available in three different cabinet colors -the standard Marvair beige, white
and gray. The standard cabinet’s sides, top and front panels are constructed of 20 gauge painted steel. As
an option, these panels can be built of 16 gauge steel in beige & gray or .050 stucco aluminum. When
the 16 gauge painted steel or the aluminum is used, only the side, top and front panels are 16 gauge or
aluminum. Contact your Marvair representative for color chips. The cabinet can also be constructed of
type 316 stainless steel. Two stainless steel cabinet constructions are available- the complete cabinet,
including most internal sheet metal or only the exterior sheet metal
1.7 Electrical Operation
The compressor and condenser fan are energized with a contactor controlled by a 24 VAC pilot signal.
Some compressors incorporate an internal PTC crankcase heater that functions as long as primary power
is available. The heater drives liquid refrigerant from the crankcase and prevents loss of lubrication
caused by oil dilution. Power must be applied to the unit for 24 hours before starting the compressor.
The condenser (outside fan) motor is energized by the same contactor. However, the motor is cycled on
and off by the low ambient control (see low ambient control 1.6).
The indoor evaporator fan motor is controlled by the fan purge on the electronic control board.

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Figure 1a. Typical Electrical Schematic - (Non-Economizer) Model MAA

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Figure 1b. Typical Electrical Schematic - (Economizer) Model MAA

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Figure 1c. Typical Electrical Schematic - (Economizer) Model MAA (Alternate Construction)

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Figure 1d. Typical Electrical Schematic - (Economizer) Model MAA (Alternate Construction)

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
 
Figure 1e. Typical Electrical Schematic - (Economizer), Model MAA (Alternate Construction)

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1.8 Economizer Components (Economizer Equipped Models Only)
Damper Actuator:
The damper actuator is a 24V motor that modulates the position of the damper blade. It is capable
of driving a full 90 degrees within 90 seconds. The assembly has a spring return to close the damper
during power outage.
Economizer changeover control (W1 Jumper)
The economizer can be controlled by either an enthalpy sensor or a dry bulb sensor. On a call for
cooling from the wall-mounted thermostat, if outdoor conditions are suitable, the sensor will open the
damper and admit outside air (i.e., economizer free cooling). If the outdoor ambient is too hot or humid
(enthalpy sensor only), the sensor will place the actuator in the closed or minimum open position and
activate mechanical cooling. The compressor is locked-out during the economizer cooling mode.
During the testing of the air conditioner at the factory, the control board has been congured for the
sensor in the air conditioner. There should be no need to change the sensor conguration. If an enthalpy
sensor is being used, pins 1 & 2 should be jumpered on the board. If a dry bulb sensor is being used,
pins 2 & 3 should be jumpered. See item 1 in Figure 4 for the location of this jumper.
Economizer changeover control setting - Enthalpy Sensor
The enthalpy sensor responds to the total heat content of the outdoor air to provide the changeover
to outside air for free cooling. The control board must be congured for proper operation of the
economizer by selecting the desired changeover temperature. The desired temperature is selected
by four dip switches on the board. See item 9 in Figure 4 for the location of the dip switches.
1. Selecting the set point for the enthalpy sensor. On the board there are four dip switches – 1, 2,
3 & 4 - that determine the ambient temperature at which the economizer damper opens. These
dip switches correspond to the following temperatures:
DIP Switch # Previous Honeywell controller setting Temperature °F/°C
All 4 Switches Down A73°/23.8°C
1 A 73°/23.8°C
2B 70°F/21.1°C
3C 67°F/19.4°C
4D 63°F/17.2°C
2. Gently push the dip switch UP to select the desired set point temperature. The factory setting is
for dip switches number 1, 2, & 3 to be in the Down position and #4 to be in the Up position.
With dip switch #4 in the Up position, the economizer damper will begin to open when the
ambient temperature is 63°F/17.2°C.
3. Only one switch should be in the Up position.
Note: having all four switches in the down position is the same setting as having the #1 switch
in the Up position.
DANGER
Sever hazard. The economizer contains moving parts capable of causing
serious injury or death. Disconnect power before removing the covering panel.
Economizer changeover control – Dry Bulb Sensor
The dry bulb sensor only responds to the dry bulb temperature of the outside air and ignores the humidity.
The sensor has eight set points. The factory setting is 58°F (14.5°C). These set points can be changed
by moving the dip switches on the top of the dry bulb sensor. See Fig. 2.

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Figure 2. Dry Bulb Sensor
Once either the enthalpy or dry bulb sensor has determined that the outside air is suitable for cooling,
the damper will open. The mixed air sensor will limit the air temperature delivered to the space by
modulating the damper blade to mix warm indoor air with cooler outdoor air to provide a constant
50°F to 56°F (10°C to 13.5°C)
Mixed Air Sensor:
The mixed air sensor is a thermistor mounted on a bracket adjacent to the right side of the blower
assembly. The thermistor senses the air temperature entering the structure, and provides a signal to the
economizer controller for modulating the position of the damper.
Minimum Position Potentiometer (W2 jumper):
The potentiometer controls the amount of outside air introduced in the building when the economizer
damper closes or the air conditioner is Off or in Mechanical Cooling. The factory setting is for the
damper to close completely when the unit is off or in Mechanical Cooling. (Pins 1 & 2 are jumpered)
If outside air is desired during mechanical cooling or whenever the indoor blower is running, jumper
pins 2 & 3. Refer to item 8 in Figure 4 for the location of the jumper.
If the potentiometer is enabled, the next step is to select how much outside air should be brought into
the building.
The potentiometer is adjustable from 0% to 100%. Setting the potentiometer to MIN means that the damper
will close completely and NO outside air will be brought into the building. Setting the potentiometer
to MAX means that the damper stays in the full OPEN position at all times. Factory setting is 50%.

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Brand of Sensor Selection (W3 jumper)
Honeywell enthalpy and dry bulb sensors are currently the only brand of sensors used in the air conditioners.
Jumper W3 allows us to use alternative brands at a future date. On all current air conditioners, pins 1
& 2 are jumpered on W3. See item 4 in Figure 4.
Figure 3. Enthalpy Sensor Temperature Control Points
Marvair Economizer Controller
Figure 4. Electrical Controls, MAA Alternate Construction

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1 2 3 4
5
6
7
89
1. W1 Economizer Sensor Selector
Jumper Pins 1 & 2 for enthalpy sensor
Jumper Pins 2 & 3 for dry bulb sensor
4. W3 Sensor Brand Selector
Jumper Pins 1 & 2 for Honeywell sensor
Jumper Pins 2 & 3 for Prism sensor
7. Minimum Position Potentiometer
0% to 100%. Factory setting is 50%.
2. Field connection from
CommStat 4 (2) terminal
5. For Honeywell sensors 8. W2 Minimum Position
Potentiometer Jumper
Jumper Pins 1 & 2 to Disable (Factory setting)
Jumper pins 2 & 3 to Enable
3. Field connection from CommStat 4
(MAR) terminal
6. For Prism sensors 9. Enthalpy Dip Switches
Set points are same as previous
Honeywell controller.
Factory setting is 4 (63°F/17.2°)
1=A (73°F/23.8°C) 2=B (70°F/21.1°C)
3=C (67°F/19.4°C) 4=D (63°F/17.2°)
Figure 5. Economizer Control Board