Midea ATOM B Series User manual



Model:
B Series
MDV‐V28WDHN1(AtB)
MDV‐V36WDHN1(AtB)
MDV‐V42WDHN1(AtB)
MDV‐V48WDHN1(AtB)
MDV‐V56WDHN1(AtB)
MDV‐V60WDHN1(AtB)
CommercialAirConditioners
R410A
Service
Manual


AtomBSeriesVRF50/60Hz
1
CONTENTS

CONTENTS


Part 1 General Information............................................................................3
Part 2 Component Layout and Refrigerant Circuits.....................................7
Part 3 Control...............................................................................................15
Part 4 Field Settings.....................................................................................23
Part 5 Electrical Components and Wiring Diagrams..................................32
Part 6 Diagnosis and Troubleshooting.........................................................45




AtomBSeriesVRF50/60Hz  
2  
MideaAtomBSeriesServiceManual


Atom B Series VRF 50/60Hz
3
Part 1 – General Information
Part 1
General Information
1 Indoor and Outdoor Unit Capacities........................................................... 4
2 External Appearance.................................................................................. 5
3 Combination Ratio..................................................................................... 6

Atom B Series VRF 50/60Hz
4
Midea Atom B Series Service Manual
1Indoor and Outdoor Unit Capacities
1.1 Indoor Units
Table 1-1.1: Indoor unit abbreviation codes
Abbreviation code
Type
Q1
One-way Cassette
Q4C
Compact Four-way Cassette
Q4
Four-way Cassette
T1
High Static Pressure Duct
T2
Medium Static Pressure Duct
G
Wall-mounted
DL
Ceiling and Floor
Table 1-1.2: Indoor unit capacity range
Capacity
Capacity
index
Q1
Q4C
Q4
T1
T2
T2(Arc)
G
DL
kBtu/h
kW
HP
5
1.5
0.5
5
—
5
—
—
—
5
—
—
6
1.8
0.6
6
6
—
—
—
—
—
—
—
7
2.2
0.8
7
7
7
—
—
7
7
7
—
9
2.8
1
9
9
9
9
—
9
9
9
—
12
3.6
1.25
12
12
12
12
—
12
12
12
12
15
4.5
1.6
15
15
15
15
—
15
15
15
15
18
5.6
2
18
18
—
18
—
18
18
18
18
24
7.1
2.5
24
24
—
24
24
24
24
24
24
28
8.0
3
28
—
—
28
28
28
—
28
28
32
9.0
3.2
32
—
—
32
32
32
—
32
32
36
10.0
3.6
36
—
—
36
—
—
—
—
36
40
11.2
4
40
—
—
40
40
40
—
—
40
48
14.0
5
48
—
—
48
48
48
—
—
48
56
16.0
6
56
—
—
56(DC)
56
56
—
—
—
Notes:
1. Atom series indoor units could connect to Atom series outdoor units.
1.2 Outdoor Units
Table 1-1.3: Outdoor unit capacity range
Capacity (kBtu/h)
Model Name
28
MDV-V28WDHN1(AtB)
36
MDV-V36WDHN1(AtB)
42
MDV-V42WDHN1(AtB)
48
MDV-V48WDHN1(AtB)
56
MDV-V56WDHN1(AtB)
60
MDV-V60WDHN1(AtB)
Notes:
1. Atom series outdoor units could not be combined.

Atom B Series VRF 50/60Hz
5
Part 1 – General Information
2External Appearance
2.1 Indoor Units
Table 1-2.1: Indoor unit appearance
One-way Cassette
Four-way Cassette
Q1
Q4
Compact Four-way Cassette
Wall-mounted
Q4C
G
High Static Pressure Duct
Medium Static Pressure Duct
T1
T2
Medium Static Pressure Duct (Arc Series Duct)
Ceiling and Floor
T2
DL
2.2 Outdoor Units
Table 1-2.2: Outdoor unit appearance
28kBtu/h
36/42/48/56kBtu/h
60kBtu/h

Atom B Series VRF 50/60Hz
6
Midea Atom B Series Service Manual
3Combination Ratio
Table 1-3.1: Indoor and outdoor unit combination ratio limitations
Type
Minimum combination ratio
Maximum combination ratio
Atom Series outdoor units
45%
130%
Table 1-3.2: Combinations of Indoor and outdoor units
Outdoor unit capacity
Sum of capacity indexes of
connected indoor units (standard
indoor units only)
Number of connected
indoor units
kBtu/h
Capacity
index
28
28
12.6 to 36.4
1-4
36
36
16.2 to 46.8
1-6
42
42
18.9 to 54.6
1-7
48
48
21.6 to 62.4
1-8
56
56
25.2 to 72.8
1-9
60
60
27.0 to 78.0
1-9
Combination ratio =
Sum of capacity indexes of the indoor units
Capacity index of the outdoor unit

‐i   AtomBSeriesVRF50/60Hz
7
Part2–ComponentLayoutandRefrigerantCircuits
Part2
ComponentLayoutand
RefrigerantCircuits

1PipingDiagrams.........................................................................................8
2RefrigerantFlowDiagrams.......................................................................11



AtomBSeriesVRF50/60Hz  
8  
MideaAtomBSeriesServiceManual
1 PipingDiagrams
Figure2‐1.1:28modelpipingdiagram


Figure2‐1.2:36modelpipingdiagram












Oil
return
hole
Temperature
sensor
Distributor
Liquid pipe
Temperature
sensor
4 way valve
Gas pipe
Compressor
Temperature
sensor
Low pressure switch
Accumulator
Refrigerant
radiator
module
Temperature
sensor
Filter
Filter
Oil return capiliary
Oil seperator
DC motor
Silencer
High pressure switch
Temperature
sensor
Distributor
Liquid pipe
Temperature
sensor
4 way valve
DC motor
Gas pipe
Compressor
Temperature
sensor
Low pressure switch
A
ccumulator
Refrigerant
radiator
module
Temperature
sensor
Filter
Filter
Oil return capiliary
Oil sepetator

‐i   AtomBSeriesVRF50/60Hz
9
Part2–ComponentLayoutandRefrigerantCircuits
Figure2‐1.3:42modelpipingdiagram


Figure2‐1.3:48/56modelpipingdiagram





High pressure
switch
Temperature
sensor
Distributor
Liquid pipe
Temperature
sensor
4 way valve
DC motor
Gas pipe
Compressor
Temperature
sensor
Low pressure switch
Accumulator
Refrigerant
radiator
module
Temperature sensor
Oil return capiliary
Oil seperator
Filter
Electronic
expansion
valve

High pressure
switch
Temperature
sensor
Distributor
Liquid pipe
Temperature
sensor
4 way valve
DC motor
Gas pipe
Compressor
Temperature
sensor
Low pressure switch
Accumulator
Refrigerant
radiator
module
Temperature sensor
Oil return capiliary
Oil seperator
Filter
Electronic
expansion
valve

AtomBSeriesVRF50/60Hz  
10  
MideaAtomBSeriesServiceManual
Figure2‐1.3:60modelpipingdiagram

Keycomponents:
1. Oilseparator:
Separatesoilfromgasrefrigerantpumpedoutofthecompressorandquicklyreturnsittothecompressor.Separation
efficiencyisupto99%.
2. Gas‐liquidseparator: 
Storesliquidrefrigerantandoiltoprotectcompressorfromliquidhammering.
3. Electronicexpansionvalve(EXV):
Controlsrefrigerantflowandreducesrefrigerantpressure.
4. Four‐wayvalve(ST1): 
Controlsrefrigerantflowdirection.Closedincoolingmodeandopeninheatingmode.Whenclosed,theheatexchanger
functionsasacondenser;whenopen,theheatexchangerfunctionsasanevaporator.
5. Highandlowpressureswitches: 
Regulatesystempressure.Whensystempressurerisesabovetheupperlimitorfallsbelowthelowerlimit,thehighor
lowpressureswitchesturnoff,stoppingthecompressor.After5minutes,thecompressorrestarts.

High pressure
switch
Temperature sense
Distributor
Liquid pipe
Temperature sense
Filter
4 way valve
DC motor
Gas pipe
Compressor
Temperature
sense
Low pressure
switch
Refrigerant
radiator
modile
Temperature sense
Oil return capiliary
42
Oil seperator
Silencer（Reserved）

‐i   AtomBSeriesVRF50/60Hz
  11
Part2–ComponentLayoutandRefrigerantCircuits
2 RefrigerantFlowDiagrams
Coolingoperation
Figure2‐2.1:28/36/42/48/56/60modelsrefrigerantflowduringcoolingoperation

Oilreturnoperationincoolingmode
Figure2‐2.4:28/36/42/48/56/60modelsrefrigerantflowduringoilreturnoperationincoolingmode



AtomBSeriesVRF50/60Hz  
12  
MideaAtomBSeriesServiceManual
Heatingoperation
Figure2‐2.7:28/36/42/48/56/60modelsrefrigerantflowduringheatingoperation


Oilreturnoperationinheatingmode
Figure2‐2.10:28/36/42/48/56/60modelsrefrigerantflowduringoilreturnoperationinheatingmode



‐i   AtomBSeriesVRF50/60Hz
  13
Part2–ComponentLayoutandRefrigerantCircuits
Defrostingoperation
Figure2‐2.13:28/36/42/48/56/60modelsrefrigerantflowduringdefrostingoperation



AtomBSeriesVRF50/60Hz  
14  
MideaAtomBSeriesServiceManual


AtomBSeriesVRF50/60Hz
  15
Part3‐Control
Part3
Control

1GeneralControlSchemeFlowchart..........................................................16
2StopOperation........................................................................................17
3StartupControl........................................................................................17
4NormalOperationControl.......................................................................18
5ProtectionControl...................................................................................19
6SpecialControl.........................................................................................21



AtomBSeriesVRF50/60Hz   
16  
MideaAtomBSeriesServiceManual
1 GeneralControlSchemeFlowchart
Sections3-2to3-7onthefollowingpagesdetailwheneachofthecontrolsintheflowchartbelowisactivated. 


Legend
Numbersinthetopright-hand
cornersofboxesindicatethe
relevantsectionoftextonthe
followingpages.
Conditionsmet
foroilreturn
Conditionsmet
fordefrosting
Specialcontrol
Oilreturnoperation
Defrostingoperation
6
Stopoperation
Abnormalshutdown
Systemstop
2
Startupcontrol
Compressorstartupdelaycontrol 
Startupcontrolforcoolingoperation
Startupcontrolforheatingoperation
3
Thermoon
Normaloperationcontrol
Componentcontrolduringnormaloperation
Compressoroutputcontrol
Compressorstepcontrol
Electronicexpansionvalvecontrol
4
Protectioncontrol
Highpressureprotectioncontrol
Lowpressureprotectioncontrol
Dischargetemperatureprotectioncontrol
Compressorprotectioncontrol
Disableheatingcontrol
5

AtomBSeriesVRF50/60Hz
  17
Part3‐Control
2 StopOperation
Thestopoperationoccursforoneofthetwofollowingreasons:
1. Abnormalshutdown:inordertoprotectthecompressors,ifanabnormalstateoccursthesystemmakesa'stopwith
thermooff'operationandanerrorcodeisdisplayedontheoutdoorunitdigitaldisplays.
2. Thesystemstopswhenthesettemperaturehasbeenreached.

3 StartupControl
3.1 CompressorStartupDelayControl
WhentheODUispoweredonagainandthecompressordelaysabout7minutestostart.Afterthecompressorstopsrunning,
ittakesabout4minutestorestart,inordertopreventfrequentcompressoron/offandtoequalizethepressurewithinthe
refrigerantsystem.
3.2 StartupControlforCoolingOperation
Table3‐3.1:Componentcontrolduringstartupincoolingmode
Component Wiring
diagramlabel 28‐60model Controlfunctionsandstates
Invertercompressor  COMP ●Controlled according to load requirement, operating
frequencyincreasedby1step/sec
DCfanmotor  FAN ●
Theoutdoorunitfanstartby14gearsfor20secondsbefore
compressor start, and then maintain the fan speed for
another 20 seconds when compressor start, finally the fan
speed controlled according to heat exchanger temperature
(T3), outdoor ambient temperature (T4) ,discharge
temperature(T5)andcompressorfrequency.
Electronicexpansionvalve  EEV ●Maintain304(step)for3minutesbeforecompressorstartup，
thencontrolledaccordingtodischargetemperature
Four-wayvalve ST1 ●Off

3.3 StartupControlforHeatingOperation
Table3‐3.2:Componentcontrolduringstartupinheatingmode
Component Wiring
diagramlabel 28‐60model Controlfunctionsandstates
Invertercompressor  COMP ●Controlled according to load requirement, operating
frequencyincreasedby1step/sec 
DCfanmotor  FAN ●
Theoutdoorunitfanstartby14gearsfor20secondsbefore
compressor startup, and then maintain the fan speed for
another 20 seconds when compressor start, finally the fan
speed controlled according to heat exchanger temperature
(T3),outdoorambienttemperature(T4)andcompressor
frequency.
Electronicexpansionvalve  EEV ●
Maintain 304 step(model 28/42) or 480 step(model
36/48/56/60)for3minutesbeforecompressorstartup,then
controlledaccordingtodischargetemperature
Four-wayvalve ST1 ●On


AtomBSeriesVRF50/60Hz  
18  
MideaAtomBSeriesServiceManual
4 NormalOperationControl
4.1 ComponentControlduringNormalOperation
Table3‐4.1:Componentcontrolduringnormalcoolingoperation
Component Wiringdiagram
label 28‐60model Controlfunctionsandstates
Invertercompressor  COMP ● Controlledaccordingtoloadrequirement
DCfanmotor  FAN ●
Fanspeedcontrolledaccordingtoheatexchangertemperature
(T3),outdoorambienttemperature(T4),dischargetemperature
(T5)andcompressorfrequency.
Electronicexpansionvalve  EEV ●Controlledaccordingtodischargetemperature
Four-wayvalve ST1 ●Off
Table3‐4.2:Componentcontrolduringheatingoperation
Component Wiringdiagram
label 28‐60model Controlfunctionsandstates
Invertercompressor  COMP ● Controlledaccordingtoloadrequirement
DCfanmotor  FAN ●
Fanspeedcontrolledaccordingtooutdoorunitheatexchanger
refrigeranttemperature(T3),outdoorambienttemperature(T4)
andcompressorfrequency.
Electronicexpansionvalve  EEV ●Controlledaccordingtodischargetemperature
Four-wayvalve ST1 ●On

4.2 CompressorOutputControl
Thecompressorrotationspeediscontrolledaccordingtotheloadrequirement.Beforecompressorstartup,theoutdoor
unitfirstestimatestheindoorunitloadrequirementaccordingtothenominalcapacityofindoorunitscurrentlyrunning,
andthencorrectforambienttemperature.Thecompressorsthenstartupaccordingtothecorrectedloadrequirement. 
Duringoperationthecompressorsarecontrolledaccordingtothenominalcapacityofindoorunitscurrentlyrunningand
theindoorunitheatexchangertemperatures.
4.3 CompressorStepControl
Therunningspeedofthecompressorsinrotationspersecond(rps)isonethirdofthefrequency(inHz)oftheelectrical
inputtothecompressormotors.Thecompressorspeedcanbealteredinincrementsof1rps.
4.4 ElectronicExpansionValveControl
ThepositionofelectronicexpansionvalvesEXViscontrolledinstepsfrom0(fullyclosed)to480(fullyopen). 
Incoolingmode:
 Whentheoutdoorunitisinstandby:
 EXVisatposition304(steps)(model28/42)or480(steps)(model36/48/56/60).
 Whentheoutdoorunitisrunning:
 EXViscontrolledaccordingtodischargetemperature(After3minutesinstandbymode).
Inheatingmode:
 Whentheoutdoorunitisinstandby:
 EXVisatposition304(steps)(model28/42)or480(steps)(model36/48/56/60).
 Whentheoutdoorunitisrunning:
 EXViscontrolledaccordingtodischargetemperature(After3minutesinstandbymode).


 AtomBSeriesVRF50/60Hz 
  19
Part3‐Control
5 ProtectionControl
5.1 HighPressureProtectionControl(excludemodel28)
Thiscontrolprotectsthesystemfromabnormallyhighpressureand protects the compressors from transient spikes in
pressure.
Figure3‐5.1:Highpressureprotectioncontrol 
Notes: 
1. P
c
:Dischargepressure 
Whenthedischargepressurerisesabove4.4MPathesystemdisplaysP1protectionandtheunitstopsrunning.Whenthe
dischargepressuredropsbelow3.2MPa,thecompressorentersre-startcontrol. 
5.2 LowPressureProtectionControl
Thiscontrolprotectsthesystemfromabnormallylowpressureand protects the compressors from transient drops in
pressure.
Figure3‐5.2:Lowpressureprotectioncontrol 
Notes: 
1. P
e
:Suctionpressure 
Whensuctionpipepressuredropsbelow0.05MPathesystemdisplaysP2protectionandtheunitstopsrunning.Whenthe
suctionpipepressurerisesabove0.14MPa,thecompressorentersre-startcontrol.
5.3 DischargeTemperatureProtectionControl
This control protects the compressors from abnormally high temperatures and transient spikes in temperature. It is
performedforeachcompressor.
Figure3‐5.3:Highdischargetemperatureprotectioncontrol 


Whenthedischargetemperaturerisesaboveorequalto115°CthesystemdisplaysP4protectionandtheunitstopsrunning.
Whenthedischargetemperaturedropsbelow90°C,thecompressorentersre-startcontrol.
Pc>4.4MPa Pc<3.2MPa
Normaloperation
Highpressureprotection,errorcodeP1isdisplayed
Pe<0.05MPa Pe>0.14MPa
Normaloperation
Lowpressureprotection,errorcodeP2isdisplayed
Dischargetemperature≥115°C  Dischargetemperature<90°C 
Normaloperation
Highdischargetemperatureprotection,errorcodeP4isdisplayed