Airxcel Marvair MGA3090A User manual

Marvair MGA3090-3210 Wall Mount AC I&O Manual 03/2021 Rev.6
Part #03836
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.
Manufactured By:
Marvair Division of the AIRXCEL®Commercial Group
P.O. Box 400 • Cordele, Georgia 31010 • 156 Seedling Drive • Cordele, Georgia 31015
[phone] • Fax [phone]
www.Marvair.com
The most current version of this manual can be found at www.Marvair.com.
MODELS:
MGA3090A & MGA3120A
(Dual Compressor)
Installation & Operation Manual
10 EER Vertical Wall-Mount Air Conditioners
Installation & Operation Manual
10EER 7.5 & 10 Ton Vertical Wall Mount
Air Conditioners

2
Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
How To Use This Manual
This manual is intended to be a guide to Marvair's line of vertical air conditioners. It contains installation, troubleshoot-
ing, 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 air conditioner 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 air conditioner 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 1-229-273-9558 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 ordi-
nances.
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 air conditioning unit and in the instruction
manuals be alert to the potential for personal injury. Understand the signal word DANGER, WARNING and
CAUTION. 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 info that will result in improved installation, reliability or operation.
© 03/2021 Marvair® Div. Airxcel™, Inc.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE.

3Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
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 Air Conditioner Description & Specications
1.1 General Description .................................................................................................................................5
1.2 Model Identication .................................................................................................................................6
1.3 Serial Number Date Code ........................................................................................................................6
1.4 Capacities, Weights and Filter Sizes ........................................................................................................6
1.5 General Operation ....................................................................................................................................9
1.6 Programmable Logic Controller (PLC) ...................................................................................................9
1.7 Unit Operation........................................................................................................................................11
1.8 Optional Controls and Packages ............................................................................................................13
1.9 Electrical Operation ...............................................................................................................................13
Chapter 2 Electronic Control Board
2.1 Introduction ............................................................................................................................................15
2.2 Installation and Replacement .................................................................................................................16
2.3 Operation................................................................................................................................................16
2.4 Sequence of Operation ...........................................................................................................................20
Chapter 3 Installation
3.1 Equipment Inspection.............................................................................................................................26
3.2 Installation Requirements.......................................................................................................................26
3.3 Installation Materials .............................................................................................................................27
3.4 Porting and Duct Work ..........................................................................................................................29
3.5 Top Flange Installation ..........................................................................................................................29
3.6 Installing the Lifting Brackets................................................................................................................30
3.7 Mounting the Unit .................................................................................................................................30
3.8 Electrical Connections ...........................................................................................................................31
Chapter 4 Start-Up
4.1 Check-Out of Cooling Cycle .................................................................................................................35
4.2 Check-Out of Heating Cycle..................................................................................................................35

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Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
Table of Contents
Chapter 5 Troubleshooting
5.1 Overview ................................................................................................................................................36
5.2 Failure Symptoms Guide........................................................................................................................37
5.3 Compressor Troubleshooting .................................................................................................................37
Chapter 6 Maintenance
6.1 Scheduled Maintenance .........................................................................................................................39
Chapter 7 Warranty
7.1 Limited Product Warranty ......................................................................................................................40
Chapter 8 Start-Up Check List
8.1 Start-Up Check List................................................................................................................................41
Illustrations
Figure 1. PLC ............................................................................................................................................10
Figure 2. Typical Electrical Schematic......................................................................................................14
Figure 3a. Setting the Speed for the Y1 and Y2 Operation for Indoor Motor ............................................17
Figure 3b. Second Stage Cooling Speed .....................................................................................................17
Figure 4. Output Termination for Indoor Motor Control Signal ...............................................................18
Figure 5. Outdoor Motor Speed Setting ....................................................................................................18
Figure 6. Output Termination for Outdoor Motor Control Signal.............................................................18
Figure 7. Communications SetUp .............................................................................................................19
Figure 8. Top Flange and Lifting Bracket Installation ..............................................................................30
Figure 9. Wall Mounting Detail.................................................................................................................31
Figure 10a. Thermostat Connection Diagram ...............................................................................................34
Figure 10b. CommStat™ 3 Wiring Detail.....................................................................................................34
Tables
Table 1 Efciency and Capacity Ratings at ANSI/AHRI Standard 390..................................................... 7
Table 2 Sensible Capacities - Single Compressor ...................................................................................... 7
Table 3 Sensible Capacities - Dual Compressor......................................................................................... 7
Table 4 Single Compressor Cooling Performance (BTUH) at Various Outdoor Temperatures ................. 8
Table 5 Dual Compressor Cooling Performance (BTUH) at Various Outdoor Temperatures.................... 8
Table 6 Economizer Cooling Performance................................................................................................. 8
Table 7 Return Air Filter Sizes ................................................................................................................... 8
Table 8 Shipping Weights & Dimensions............................................................................................................. 8
Table 9 MODBUS Network Address DIP Swith Positions ...................................................................... 20
Table 10a. MODBUS Discrete Registers ...................................................................................................... 24
Table 10b. MODBUS Registers..................................................................................................................... 25
Table 11 Minimum Clearances................................................................................................................... 27
Table 12 Voltage Limitations ...................................................................................................................... 27

5Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
Chapter 1 Description & Specications
1.1 General Description
The Marvair MGA3090A & MGA3120A are a series of vertical wall-mounted air conditioning
systems that provide heating, cooling, and ventilation for telecommunication shelters, and other
applications with high internal heat gains. The series is available in nominal cooling capacities of
90,000-120,000 BTUH. A factory installed economizer, resistance heating elements and reverse ow
congurations are available.
All Marvair MGA wall mount air conditioners feature an exclusive electronic control board or PLC-
based controls.
The control board and PLC consolidate several of the electrical components, improves the air
conditioner’s reliability and has LED’s to indicate operating status and fault conditions to assist the
service technician. A complete description of functions is in Section 1.6
Other standard components include:
• Hot gas by-pass valve to allow operation in cold temperatures
• Thermal expansion valve to improve both efciency and capacity over a wide range of ambient
temperatures
• Phase monitor to prevent operation if the unit is not properly phased
Marvair air conditioners are designed for easy installation and service. Major components are accessible
for service beneath external panels.
All units have internal disconnects. Depending upon state and local code requirements, this feature
may eliminate the need for an external breaker or disconnect.

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Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
1.2 Model Identication
The model identication number is found on the data sticker. Rating plate located on side panel.
Example M G A 3 0 9 0 A D 1 5 0 C + + + + 1 C A + A 1 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) G = 10
3Refrigerant Type A = R-410a
4Compressor Type/
Quantity
1 = Single
3 = Dual Compressors
5Unit Capacity/Nominal
Cooling (BTUH)
090 = 90,000
120 = 120,000
6
7
8System Type A = Air Conditioner
9Power Supply
(Volts-Phase-Hz)
A= 208/230-1-60
C= 208/230-3-60
D= 460-3-60
E= 380-3-50 - 4 Wire
F= 220-1-50
Z= 575-3-60
10 Heat Designation
@ Rated Voltage
KW = Kilowatt
000 = No Heat
050 = 5KW
090 = 9KW
150 = 15KW
180 = 18KW
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
14 Dehumidication
R = Electric Reheat
T = Electric Reheat w/Humidity Control
+ = None
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
F = ModBus Interface
G = ModBus Interface
w/Factory Installed T-Stat
H = Bac-Net
J = Bac-Net Controls
w/Factory Installed T-Stat
+ = None
16 Operating Condition
A = Evaporator Freeze Sensor (EFS)
C = EFS w/Hot Gas Bypass
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
17 Indoor Air Quality
Features
D = Dry Bulb Sensor
E = Dry Bulb Sensor w/Dirty Filter
G = Dirty Filter Sensor
+ = None
18 Air Flow 1 = Top Supply/Bottom Return
2 = Center Supply (Reverse)
19 Compressor
Location
C = Center
D = Left Hand
E = Right Hand
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
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
K = Coastal Package
+ = None
$ = Special
22 Engineering
Revision Level A1
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
+ = None
27 Fastener/Drain Pan
Option
A = Stainless Steel Fasteners
C = Stainless Steel Drain Pan
D = Stainless Steel Fasteners & Drain Pan
E = IP55 Ingress
+ = None
28 Unused + = None
$ = Special
29 Unused + = None
$ = Special
30 Special Variation
+ = None
$ = Special Conguration Not Covered by
Model Nomenclature
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 Capacities, Weights and Filter Sizes
See the Product Data Sheet for complete electrical and performance specications and dimensional
drawings.

7Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
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.
Basic Model Cooling BTUH1EER2Rated Air Flow (CFM)3
MGA3090A 89,000 10 3,500
MGA3120A 118,000 10 4,000
1Cooling rated at 95°F (35°C) outdoor and 80°F DB/67° WB (26.5°C DB/19.5°C WB) return air. 2EER=Energy Efciency Ratio
3CFM=Cubic Feet per Minute
Ratings are with no outside air. Performance will be affected by altitude.
Ratings are at 230 volts for 208/230 volt units (“A” & “C” models) and 460 volts for “D” models. Operation of units at a different voltage
from that of the rating point will affect performance and air ow.
Table 1. Efficiency and Capacity Ratings at ANSI/AHRI Standard 390
MGA3090A (Stage 1)
Return Air DB/WB Sensible Cooling
Capacity
Outside Air Temperature ºF (ºC)
75 (24) 80 (27) 85 (30) 90 (32) 95 (35)
79/66
BTUH
40,953 40,416 39,874 39,339 38,800
75/61 42,039 40,581 39,164 37,706 36,248
80/63 43,700 42,201 40,662 39,164 37,665
85/65 45,320 43,781 42,201 40,662 39,083
MGA3120A (Stage 1)
Return Air DB/WB Sensible Cooling
Capacity
Outside Air Temperature ºF (ºC)
75 (24) 80 (27) 85 (30) 90 (32) 95 (35)
79/66
BTUH
68,061 65,732 63,372 61,043 58,684
75/61 61,999 59,848 57,758 55,608 53,457
80/63 64,448 62,238 59,968 57,758 55,548
85/65 66,837 64,567 62,238 59,968 57,638
Table 2. Sensible Capacities - Single Compressor Operation
MGA3090A (Stage 2)
Return Air
DB/WB
Sensible Cooling
Capacity
Outside Air Temperature ºF (ºC)
75 (24) 80 (27) 85 (30) 90 (32) 95 (35) 100
(38)
105
(41)
110
(43)
115
(46)
120
(49)
125
(52)
130
(54)
79/66*
BTUH
74,445 73,149 71,827 70,547 69,274 67,701 66,718 65,451 64,829 64,256 63,684 63,114
75/61 77,983 76,678 75,416 74,126 72,843 71,567 70,298 69,071 68,443 66,928 65,326 63,724
80/63 87,060 85,763 84,439 83,158 81,884 79,477 76,184 72,802 71,200 69,598 67,996 66,394
85/65 96,006 94,720 92,738 89,356 85,885 82,414 79,032 75,561 73,870 72,268 70,666 69,064
MGA3120 (Stage 2)
Return Air
DB/WB
Sensible Cooling
Capacity
Outside Air Temperature ºF (ºC)
75 (24) 80 (27) 85 (30) 90 (32) 95 (35) 100
(38)
105
(41)
110
(43)
115
(46)
120
(49)
125
(52)
130
(54)
79/66*
BTUH
99,115 97,304 95,482 93,696 91,900 90,117 88,369 86,611 85,748 84,954 84,162 83,373
75/61 103,575 101,753 99,994 98,197 96,412 94,639 92,878 91,178 90,307 89,440 88,462 86,293
80/63 115,351 113,540 111,693 109,907 108,134 106,373 103,166 98,586 96,417 94,247 92,078 89,909
85/65 126,948 125,152 123,321 121,003 116,303 111,602 107,023 102,322 100,032 97,863 95,694 93,524
Table 3. Sensible Capacities - Dual Compressor Operation

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Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
Basic Model Outdoor Temperature
75ºF / 24ºC 80ºF / 26.5ºC 85ºF / 29ºC 90ºF / 32ºC 195ºF / 35ºC
MGA3090A 46,980 45,360 43,740 42,120 40,500
MGA3120A 69,286 66,896 64,507 62,118 59,729
1Based upon ANSI/AHRI std. 390 return air conditions of 80°F DB/67° WB (26.5°C DB/19.5°C WB) at various outdoor temperatures.
Table 4. Single Compressor Cooling Performance (BTUH) at Various Outdoor Temperatures
Basic Model Outdoor Temperature
75ºF / 24ºC 80ºF / 26.5ºC 85ºF / 29ºC 90ºF / 32ºC 195ºF / 35ºC
MGA3090A 103,240 99,680 96,120 92,560 89,000
MGA3120A 139,804 134,984 130,163 125,342 120,521
1Based upon ANSI/AHRI std. 390 return air conditions of 80°F DB/67° WB (26.5°C DB/19.5°C WB) at various outdoor temperatures.
Table 5. Dual Compressor Cooling Performance (BTUH) at Various Outdoor Temperatures
Basic Model Fan Watts Fan CFM EER @ 55 F OAT Outside Air Temperature ºF (ºC)
50 (10) 55 (13) 60 (16) 65 (18) 70 (21)
MGA3090A 730 3,500 125 110,128 91,140 72,153 53,165 34,178
MGA3120A 967 4,000 108 125,860 104,160 82,460 60,760 39,060
Based upon indoor setpoint temperature of 79 (26).
Table 6. Economizer Cooling Performance
Model Description INCHES MILLIMETERS PART NO. FILTERS PER UNIT MERV RATING
MGA3090A Exterior Access Return Air Filter 25" x 16" x 2" 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15" x 20" x 2" 381 x 508 x 51 92365 3 8
MGA3090A
Reverse Flow
Exterior Access Return Air Filter 25” x 16” x 2” 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15” x 20” x 2” 381 x 508 x 51 92365 3 8
MGA3090A
Reverse Flow
w/Economizer
Exterior Access Return Air Filter 25” x 16” x 2” 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15” x 20” x 2” 381 x 508 x 51 92365 3 8
Economizer Pre-lter 9.25” x 37” x .375” 235 x 940 x 10 92127 1 N/A
MGA3120A
Exterior Access Return Air Filter 25” x 16” x 2” 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15” x 20” x 2” 381 x 508 x 51 92365 3 8
For Optional Fresh Air Hood, #K/04657 11” x 22” x 1” 279 x 559 x 25 80119 2 N/A
MGA3120A
Reverse Flow
Exterior Access Return Air Filter 25” x 16” x 2” 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15” x 20” x 2” 381 x 508 x 51 92365 3 8
MGA3120A
w/Economizer
Exterior Access Return Air Filter 25” x 16” x 2” 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15” x 20” x 2” 381 x 508 x 51 92365 3 8
Fresh Air Hood Pre-lters 26” x 12” x 1” 660 x 305 x 25 92526 2 N/A
MGA3120A
Reverse Flow
w/Economizer
Exterior Access Return Air Filter 25” x 16” x 2” 635 x 406 x 51 80137 3 8
Interior Access Return Air Filter 15” x 20” x 2” 381 x 508 x 51 92365 3 8
Economizer Pre-lter 9.25” x 37” x .375” 235 x 940 x 10 92127 1 N/A
Table 7. Return Air Filter Sizes
Model Unit Weight Shipping Weight Shipping Dimensions Height Width Depth
LBS KG LBS KG Inches MM Inches MM Inches MM
MGA3090A 1,085 492 1,160 527 98 2,489 56 1,422 48 1,219
MGA3090A Reverse Flow 1,085 492 1,160 527 98 2,489 56 1,422 48 1,219
MGA3090A Reverse Flow w/Economizer 1,131 513 1,210 550 98 2,489 56 1,422 48 1,219
MGA3120A 1,195 542 1,277 579 98 2,489 56 1,422 48 1,219
MGA3120A Reverse Flow 1,195 542 1,277 579 98 2,489 56 1,422 48 1,219
MGA3120A w/Economizer 1,245 565 1,331 604 98 2,489 56 1,422 48 1,219
MGA3120A Reverse Flow w/Economizer 1,245 565 1,331 604 98 2,489 56 1,422 48 1,219
Table 8. Shipping Weights & Dimensions

9Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
1.5 General Operation
Hot Gas By-Pass
Normally used in specialty applications (i.e Magnetic Resonance Imaging (MRI) buildings) to prevent
magnetic voltage disturbance caused by cycling. This technology is applied in this product to extend
the operation envelope for the compressor to 20º F (-6.6ºC). Combined with a condenser low ambient
Fan Cycle feature, compressor operation can be extended to 0º F (-17.8ºC). During Hot Gas operation
mode, system performance will be reduced. If product operation is in mild outdoor ambient conditions,
the installed shut-off ball valve may be closed, thus disabling the Hot Gas By-Pass feature.
Refrigerant Cycle (Cooling Mode)
The 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 motorized impeller 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 with a thermal
expansion valve (TXV) into the evaporator to repeat the cycle.
MGA3090A/3120A (Dual Compressor) Units: These units are factory wired for maximum cooling
utilizing both compressors. If 2 stage compressor operation is desired, the factory installed jumper
between terminals 1 and 2 of the low voltage terminal strip must be removed. The 1st stage cooling
input is terminal 1 of the low voltage terminal strip and the 2nd stage cooling input is terminal 2 of the
low voltage terminal strip. The thermostat must be programmed for 2 stage cooling operation when 2
stage compressor operation is desired.
Heating Mode
A wall-mounted thermostat controls the heating cycle of models which incorporate resistance heating
elements. On a call for heat, the thermostat closes the heat relay to energize the indoor fan and the
resistance elements.
1.6 Programmable Logic Controller (MGA3120)
MGA3120 models include a factory installed PLC to control the operation of the HVAC system (MGA3090
models are standard with the Marvair printed circuit board, see Chapter 2). LEDs on the PLC show
operational status and provide assistance with diagnosis if troubleshooting is ever required. Various
control functions are eld selectable and programmable. The PLC is also capable of communicating to
other PLCs to allow run time leveling and does not require additional equipment to be installed. The
PLC provides improved reliability because of the reduction of components. The components utilized
are more durable and the control box wiring has been simplied. Pertinent statistical data about the life
of the refrigeration system can be accessed through the PLC.
The PLC is factory installed and tested, requires no adjustments or changes when the air conditioning
system is installed.
Location
The PLC is located in the unit control panel. Remove the HVAC unit front access panel and open the
panel door to the control cabinet.

10
Marvair MGA3090-3120 I&O Manual 03/2021 Rev.6
Figure 1. Programmable Logic Controller
PLC Inputs & Outputs
e PLC has inputs located along the top right of the controller and outputs along the bottom right of
the controller. An input is a signal to the PLC from either the thermostat, sensors in the air conditioner,
or a customer supplied input, e.g., EMS (Energy Management System). An output is a signal from the
PLC to the air conditioner, to the thermostat or to the customer.
PLC Inputs
e PLC inputs are powered by 24 VDC. e inputs are:
• Y – Compressor
• Y2 – Dual Compressor
• HUM – Humidier (uses optional electric heat)
• HPS – High Refrigerant Pressure Switch. The HPS is ON during normal operation. No light indicates
an open switch. See lockout indicator “A” under Outputs. HPS B available for dual compressor
systems.
• LPS – Low Refrigerant Pressure Switch. The LPS is ON during normal operation. No light indicates
an open switch. See lockout indicator “A” under Outputs. LPS B available for dual compressor
systems.
• EMS – Energy Management System. A shutdown input from an external source. When EMS input
is de-energized, the unit compressor and fans will also de-energize.
• PMF - Phase monitor fault to monitor phase operation for 3 phase systems, light is on when 3 phase
power is powered and connected correctly
PLC Outputs
The PLC outputs are connected to 24VDC and supply 24VDC loads within the control panel. These
outputs are:
• OFM – Outdoor Fan Motor Starter
• IBM – Indoor Blower Motor Starter
• CC – Compressor Starter
• CC2 – Compressor Starter B (Dual Systems)