Mars Comfort-Aire VMH Series User manual

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Service Manual
VMH Series
Inverter Multi Zone Ductless Mini-Split
Model
A-VMH18DU-1
A-VMH28TU-1
A-VMH36QU-1
A-VMH48PU-1

Service Manual - VMH 18/28/36/48 Series
2
CONTENTS
1. Indoor Unit Combination......................................................................................................................................... 4
2. Dimension Of Outdoor Unit .................................................................................................................................... 7
3. Refrigerant Cycle Diagram....................................................................................................................................... 9
4. Installation Details .................................................................................................................................................12
4.1 Wrench torque sheet for installation ...............................................................................................................12
4.2 Connecting the cables ...................................................................................................................................... 12
4.3 Pipe length and the elevation........................................................................................................................... 12
4.4 First-Time Installation.......................................................................................................................................12
4.5 Adding Refrigerant after Long-Term System Operation...................................................................................14
4.6 Procedure when servicing the indoor unit refrigeration circuit....................................................................... 14
4.7 Evacuation after servicing the outdoor unit refrigeration circuit ....................................................................15
5. Electronic Function ................................................................................................................................................17
5.1 Abbreviation .....................................................................................................................................................17
5.2 Electric Control Working Environment............................................................................................................. 17
5.3 Main Protection................................................................................................................................................ 17
5.4 Control and Functions ...................................................................................................................................... 19
6. Wiring Diagrams.....................................................................................................................................................24
7. Troubleshooting.....................................................................................................................................................45
7.1Safety................................................................................................................................................................. 45
7.2Indoor Unit Error Display...................................................................................................................................46
7.3 Outdoor Unit Display ........................................................................................................................................48
7.4 Diagnosis and Solution .....................................................................................................................................54
7.5 Trouble Criterion of Main Parts......................................................................................................................111
8. Disassembly Instructions .....................................................................................................................................121
A-VMH18DU-1.............................................................................................................................................. 121
A-VMH18DU-1.............................................................................................................................................. 121

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A-VMH28TU-1 ..............................................................................................................................................135
A-VMH36QU-1, A-VMH48PU-1................................................................................................................. 143
A-VMH36QU-1, A-VMH48PU-1................................................................................................................. 150

Service Manual - VMH 18/28/36/48 Series
4
1. Indoor Unit Combination
Multi DC Outdoor
Unit
Nominal
capacity
Suggested
Combination Limit
A-VMH18DU-1 5.2kW
6+6
None
6+9
6+12
9+9
9+12
12+12
Multi DC Outdoor
Unit
Nominal
capacity
Suggested Combination Limit
Two units Three units
A-VMH28TU-1 7.8kW
6+12 6+6+6 6+12+12
None
6+18
6+6+9
6+12+18
9+9
6+6+12
9+9+9
9+12
6+6+18
9+9+12
9+18
6+9+9
9+9+18
12+12
6+9+12
9+12+12
12+18
6+9+18
12+12+12
18+18
A-VMH28TU-1 7.8kW
6+12
6+6+6
6+9+18
None
6+18
6+6+9
6+12+12
9+9
6+6+12
9+9+9
9+12
6+6+18
9+9+12
9+18
6+6+24
9+9+18
9+24
6+9+9
9+12+12
12+12
6+9+12
12+12+12
12+18
12+24
18+18

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Multi DC Outdoor Unit Nominal capacity Suggested Combination Limit
Two units Three units Four units
A-VMH36QU-1 10.5kW
6+18 6+6+12 9+9+12 6+6+6+6 6+9+9+18
None
6+24
6+6+18
9+9+18
6+6+6+9
6+9+9+24
9+18
6+6+24
9+9+24
6+6+6+12
6+9+12+12
9+24
6+9+12
9+12+12
6+6+6+18
6+9+12+18
12+12
6+9+18
9+12+18
6+6+6+24
6+12+12+12
12+18
6+9+24
9+12+24
6+6+9+9
6+12+12+18
12+24
6+12+12
9+18+18
6+6+9+12
9+9+9+9
18+18
6+12+18
12+12+12
6+6+9+18
9+9+9+12
18+24
6+12+24
12+12+18
6+6+9+24
9+9+9+18
24+24
6+18+18
12+12+24
6+6+12+12
9+9+12+12
6+18+24
12+18+18
6+6+12+18
9+9+12+18
9+9+9
6+6+12+24
9+12+12+12
6+9+9+9
12+12+12+12
6+9+9+12
A-VMH36QU-1 10.5kW
6+18 6+6+12 9+9+9 6+6+6+6 6+9+9+12
None
6+24
6+6+18
9+9+12
6+6+6+9
6+9+9+18
6+30
6+6+24
9+9+18
6+6+6+12
6+9+9+24
9+18
6+6+30
9+9+24
6+6+6+18
6+9+12+12
9+24
6+9+12
9+9+30
6+6+6+24
6+9+12+18
9+30
6+9+18
9+12+12
6+6+6+30
6+12+12+12
12+12
6+9+24
9+12+18
6+6+9+9
6+12+12+18
12+18
6+9+30
9+12+24
6+6+9+12
9+9+9+9
12+24
6+12+12
9+18+18
6+6+9+18
9+9+9+12
12+30
6+12+18
12+12+12
6+6+9+24
9+9+9+18
18+18
6+12+24
12+12+18
6+6+12+12
9+9+12+12
18+24
6+12+30
12+12+24
6+6+12+18
9+9+12+18
18+30
6+18+18
12+18+18
6+6+12+24
9+12+12+12
24+24
6+18+24
6+9+9+9
12+12+12+12

Service Manual - VMH 18/28/36/48 Series
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Multi DC
Outdoor Unit
Nominal
capacity
Suggested Combination
Limit
Two
units
Three units Four units Five units
A-VMH48PU-1 14kW
9+24 6+6+24 9+12+18 6+6+6+18 6+9+18+30 6+6+6+6+9 6+6+12+12+12
None
9+30
6+6+30 9+12+24
6+6+6+24
6+12+12+12
6+6+6+6+12
6+6+12+12+18
9+36
6+6+36 9+12+30
6+6+6+30
6+12+12+18
6+6+6+6+18
6+6+12+12+24
12+24
6+9+24 9+12+36
6+6+6+36
6+12+12+24
6+6+6+6+24
6+6+12+18+18
12+30
6+9+30 9+18+18
6+6+9+18
6+12+12+30
6+6+6+6+30
6+9+9+9+9
12+36
6+9+36 9+18+24
6+6+9+24
6+12+18+18
6+6+6+6+36
6+9+9+9+12
18+18
6+12+18 9+18+30
6+6+9+30
6+12+18+24
6+6+6+9+9
6+9+9+9+18
18+24
6+12+24 9+18+36
6+6+9+36
9+9+9+9
6+6+6+9+12
6+9+9+9+24
18+30
6+12+30 9+24+24
6+6+12+12
9+9+9+12
6+6+6+9+18
6+9+9+9+30
18+36
6+12+36 9+24+30
6+6+12+18
9+9+9+18
6+6+6+9+24
6+9+9+12+12
24+30
6+18+18 12+12+12
6+6+12+24
9+9+9+24
6+6+6+9+30
6+9+9+12+18
24+36
6+18+24
12+12+18
6+6+12+30
9+9+9+30
6+6+6+9+36
6+9+9+12+24
30+30
6+18+30
12+12+24
6+6+12+36
9+9+9+36
6+6+6+12+12
6+9+9+18+18
6+18+36
12+12+30
6+6+18+18
9+9+12+12
6+6+6+12+18
6+9+12+12+12
6+24+24
12+12+36
6+6+18+24
9+9+12+18
6+6+6+12+24
6+9+12+12+18
6+24+30
12+18+18
6+6+18+30
9+9+12+24
6+6+6+12+30
6+9+12+12+24
9+9+18
12+18+24
6+6+24+24
9+9+12+30
6+6+6+18+18
6+12+12+12+12
9+9+24
12+18+30
6+9+9+12
9+9+18+18
6+6+6+18+24
6+12+12+12+18
9+9+30
12+24+24
6+9+9+18
9+9+18+24
6+6+9+9+9
9+9+9+9+9
9+9+36
18+18+18
6+9+9+24
9+12+12+12
6+6+9+9+12
9+9+9+9+12
9+12+12
18+18+24
6+9+9+30
9+12+12+18
6+6+9+9+18
9+9+9+9+18
6+9+9+36
9+12+12+24
6+6+9+9+24
9+9+9+9+24
6+9+12+12
9+12+12+30
6+6+9+9+30
9+9+9+12+12
6+9+12+18
9+12+18+18
6+6+9+12+12
9+9+9+12+18
6+9+12+24
9+12+18+24
6+6+9+12+18
9+9+9+12+24
6+9+12+30
12+12+12+12
6+6+9+12+24
9+9+12+12+12
6+9+12+36
12+12+12+18
6+6+9+12+30
9+9+12+12+18
6+9+18+18
12+12+12+24
6+6+9+18+18
9+12+12+12+12
6+9+18+24
12+12+18+18
6+6+9+18+24
12+12+12+12+12

Service Manual - VMH 18/28/36/48 Series
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2. Dimension Of Outdoor Unit
H
D
A
B
Model Unit W D H W1 A B
A-VMH18DU-1 mm 845 363 702 923 540 350
inch 33.3 14.3 27.6 36.0 21.3 13.8
A-VMH18DU-1 mm 890
342
673
990
663
354
inch 35.04 13.46 26.50 38.98 26.10 13.94
A-VMH28TU-1 mm 946 410 810 1034 673 403
inch 37.2 16.5 31.9 40.6 26.5 15.9
A-VMH36QU-1
A-VMH48PU-1
mm 946 410 810 1034 673 403
inch 37.2 16.5 31.9 40.6 26.5 15.9

Service Manual - VMH 18/28/36/48 Series
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H
W
A
D
W1
B
Model
Unit
W D H W1 A B
A-VMH36QU-1
A-VMH48PU-1
mm 952 415 1333 1060 634 404
inch 37.5 16.3 52.5 41.7 25.0 15.9

Service Manual - VMH 18/28/36/48 Series
9
3. Refrigerant Cycle Diagram
3.1 Refrigeration circuit drawing of A-VMH18DU-1
LIQUID VALVE A
GAS VALVE A
HEAT
EXCHANGE
(EVAPORATOR) HEAT
EXCHANGE
(CONDENSER)
COOLING
HEATING
T2 Evaporator
temp. sensor
middle
T1 Room
temp. sensor
T3
Condenser
temp. sensor
T4 Ambient
temp. sensor
INDOOR OUTDOOR
EXV A
CAPILLARY TUBE
EXV B
LIQUID VALVE B
GAS VALVE B
Compressor
4-WAY VALVE
T5 Discharge
temp. sensor
Accumulator High pressure
switch
Low pressure
switch
T2B-A Evaporator
temp. sensor outlet
T2B-B
T2B-C

Service Manual - VMH 18/28/36/48 Series
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3.3 Refrigeration circuit drawing A-VMH28TU-1
HEAT
EXCHANGE
(EVAPORATOR) HEAT
EXCHANGE
(CONDENSER)
COOLING
HEATING
T2 Evaporator
temp. sensor
middle
T1 Room
temp. sensor
T3
Condenser
temp. sensor
T4 Ambient
temp. sensor
INDOOR OUTDOOR
CAPILLARY TUBE
EXV A
LIQUID VALVE A
GAS VALVE A
EXV B
LIQUID VALVE B
GAS VALVE B
EXV C
LIQUID VALVE C
GAS VALVE C
Compressor
4-WAY VALVE
T5 Discharge
temp. sensor
Accumulator High pressure
switch
Low pressure
switch
T2B-A Evaporator
temp. sensor outlet
T2B-B
T2B-C
3.4 Refrigeration circuit drawing of A-VMH36QU-1
LIQUID VALVE A
GAS VALVE A
HEAT
EXCHANGE
(EVAPORATOR) HEAT
EXCHANGE
(CONDENSER)
COOLING
HEATING
T2 Evaporator
temp. sensor
middle
T1 Room
temp. sensor
T3
Condenser
temp. sensor
T4 Ambient
temp. sensor
INDOOR OUTDOOR
EXV A
CAPILLARY TUBE
EXV B
LIQUID VALVE B
GAS VALVE B
EXV C
LIQUID VALVE C
GAS VALVE C
EXV D
LIQUID VALVE D
GAS VALVE D
Compressor
4-WAY VALVE
T5 Discharge
temp. sensor
Accumulator High pressure
switch
Low pressure
switch
T2B-A Evaporator
temp. sensor outlet
T2B-B
T2B-C
T2B-D

Service Manual - VMH 18/28/36/48 Series
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3.6 Refrigeration circuit drawing of A-VMH48PU-1
LIQUID VALVE A
GAS VALVE A
HEAT
EXCHANGE
(EVAPORATOR) HEAT
EXCHANGE
(CONDENSER)
COOLING
HEATING
T2 Evaporator
temp. sensor
middle
T1 Room
temp. sensor
T3
Condenser
temp. sensor
T4 Ambient
temp. sensor
INDOOR OUTDOOR
EXV A
CHECK VALVE
EXV B
LIQUID VALVE B
GAS VALVE B
EXV C
LIQUID VALVE C
GAS VALVE C
EXV D
LIQUID VALVE D
GAS VALVE D
EXV E
LIQUID VALVE E
GAS VALVE E
Compressor
4-WAY VALVE
T5 Discharge
temp. sensor
Accumulator High pressure
switch
Low pressure
switch
T2B-A Evaporator
temp. sensor outlet
T2B-B
T2B-C
T2B-D
T2B-E
EXV F
Plate heat
exchanger EXV G
Radiator for IPM

Service Manual - VMH 18/28/36/48 Series
12
4. Installation Details
4.1 Wrench torque sheet for installation
Outside diameter Torque Additional tightening torque
mm inch N.cm N.cm
Ф6.35 1/4 1500(153kgf.cm) 1600(163kgf.cm)
Ф9.52 3/8 2500(255kgf.cm) 2600(265kgf.cm)
Ф12.7 1/2 3500(357kgf.cm) 3600(367kgf.cm)
4.2 Connecting the cables
The power cord connection should be
selected according to the following
specifications sheet.
Unit AWG
1 drive 2 type (18K outdoor unit) 14
1 drive 3 type (27K outdoor unit). 14
1 drive 4 type (36K outdoor unit) 12
1 drive 5 type (48K outdoor unit) 10
For indoor unit and outdoor unit connection
line, 16AWG is ok for all.
4.3 Pipe length and the elevation
Maximum piping length and height difference
1 drive 2
1 drive 3
1 drive 4
1 drive 5
Max. length for all
rooms (m)
40
(131ft)
60
(197ft)
80
(262ft)
80
(262ft)
Max. length for
one IU (m)
25 (82ft) 30 (98ft)
35
(115ft)
35
(115ft)
Max. height
difference between
IU and OU (m)
15
(49.2ft)
15
(49.2ft)
15
(49.2ft)
15
(49.2ft)
Max. height
difference between
IUs (m)
10 (33ft) 10 (33ft) 10 (33ft) 10 (33ft)
Additional refrigerant charge
Connective Pipe Length(m)
Additional refrigerant
Liquid Side
Ø6.35 (1/4”)
Ø9.52 (3/8”)
Pre-charge pipe length
(ft/m)
(pre-charge pipe length xN
)
N/A
More than (pre-charge pipe
lengthxN) ft/m
(Total pipe
length - pre-
charge pipe
lengthxN)
x15g/m
(Total pipe length
-pre-charge pipe
lengthxN)
x30g/m
(Total pipe
length - pre-
charge pipe
lengthxN)
x0.16oZ/ft
(Total pipe length
-pre-charge pipe
lengthxN)
x0.32oZ/ft
Note:The standard pipe length is 25’
Caution:
●Refrigerant pipe diameter is different
according to indoor unit to be connected.
When using the extension pipe, refer to the
tables below.
●When refrigerant pipe diameter is different
from that of the outdoor unit connector (18K
indoor unit) an additional adapter is required.
Indoor unit
Extension pipe diameter
(mm/inch)
Model
Pipe diameter
(mm/inch)
9K
Liquid
6.35(1/4)
Liquid
6.35(1/4)
Gas
9.52(3/8)
Gas
9.52(3/8)
12K 18K
Liquid
6.35(1/4)
Liquid
6.35(1/4)
Gas
12.7(1/2)
Gas
12.7(1/2)
24K
Liquid
9.52 (3/8)
Liquid
9.52 (3/8)
Gas
15.9(5/8)
Gas
15.9(5/8)
Outdoor unit union diameter (mm/inch)
1 drive 2
Liquid
6.35(1/4) *2
Gas
9.52(3/8) *2
1 drive 3
Liquid
6.35(1/4) *3
Gas
9.52(3/8) *3
1 drive 4
Liquid
6.35(1/4) *4
Gas
9.52(3/8) *3
12.7(1/2) *1
1 drive 5
Liquid
6.35(1/4) *5
Gas
9.52(3/8) *3
12.7(1/2) *2
4.4 First-Time Installation
Air and moisture in the refrigerant system cause
the following problems:
●Increases in system pressure
●Increases in operating current
●Decreases in cooling and heating efficiency
●Blocks in capillary piping caused by moisture
in the refrigerant circuit freezing
●Corrosion of parts in the refrigerant system
caused by water
The indoor units and the pipes between
indoor and outdoor units must be tested for
leakages and evacuated to remove gas and
moisture from the system.
Gas leak check with soap water:
Apply soap water or a liquid neutral
detergent on the connections with a soft brush to
check for leakage in the pipe connecting points. If
bubbles emerge, the pipes are leaking.

Service Manual - VMH 18/28/36/48 Series
13
1. Air Purging Using the Vacuum Pump
1. Completely tighten the flare nuts on the
indoor and outdoor units. Confirm that both
the 2-way and 3-way valves are set to the
closed position.
2. Connect the charge hose with the push pin of
the Handle Lo to the 3-way valve gas service
port.
3. Connect the charge hose of the Handle Hi to
the vacuum pump.
4. Fully open the Handle Lo of the manifold
valve.
5. Turn on the vacuum pump to begin
evacuation.
6. Conduct a 30-minute evacuation. Check
whether the compound meter indicates -
0.1Mpa (14.5Psi). If the meter does not
indicate -0.1Mpa (14.5Psi) after 30 minutes
has elapsed, continue evacuation for 20 more
minutes. If the pressure does not reach -
0.1Mpa (14.5Psi) after 50 minutes has
elapsed, check if there are any leaks.
Fully close the Handle Lo valve of the manifold
valve and turn off the vacuum pump. After 5
minutes, confirm that the gauge needle is not
moving.
7. Turn the flare nut on the 3-way valve 45°
counterclockwise for 6-7 seconds. Once gas
begins to come out, tighten the flare nut.
Make sure the pressure display on the
pressure indicator is higher than atmospheric
pressure. Then remove the charge hose from
the 3-way valve.
8. Fully open the 2-way and 3-way valves and
securely tighten the cap on the 3-way valve.
2. Adding refrigerant if the pipe length
exceeds chargeless pipe length
Procedure:
1) Connect the charge hose to the charging cylinder
and open the 2-way and 3-way valves.
With the charge hose you disconnected from the
vacuum pump, connect it to the valve at the
bottom of the cylinder.
If the refrigerant is R410A, place the cylinder
bottom-up to ensure liquid charging is possible.
2). Purge the air from the charge hose.
Open the valve at the bottom of the cylinder and
press the check valve on the charge set (be
careful of the liquid refrigerant).
3) Place the charging cylinder onto the electronic
scale and record the weight.
4) Turn on the air conditioner in cooling mode.
5) Open the valves (Low side) on the charge set.
Charge the system with liquid refrigerant.
6). When the electronic scale displays the proper
weight (refer to the table), disconnect the charge
hose from the 3-way valve’s service port
immediately and turn off the air conditioner before
disconnecting the hose.
7). Mount the valve stem caps and the service port
Use a torque wrench to tighten the service port
cap to a torque of 18N.m (13.27 ft· lbs.).
Be sure to check for gas leaks.

Service Manual - VMH 18/28/36/48 Series
14
4.5 Adding Refrigerant after Long-Term
System Operation
Procedure
1) Connect the charge hose to the 3-way service
port and open the 2-way and 3-way valve.
Connect the charge hose to the valve at the
bottom of the cylinder. If the refrigerant is R410A,
place the cylinder bottom-up to ensure liquid
charge.
2). Purge the air from the charge hose.
Open the valve at the bottom of the cylinder and
press the check valve on the charge set to purge
the air (be careful of the liquid refrigerant).
3) Place the charging cylinder onto the electronic
scale and record the weight.
4) Turn on the air conditioner in cooling mode.
5) Open the valves (Low side) on the charge set
and charge the system with liquid refrigerant.
6). When the electronic scale displays the proper
weight (refer to the gauge and the pressure of the
low side), disconnect the charge hose from the 3-
way valve’s service port immediately and turn off
the air conditioner before disconnecting the hose.
7). Mount the valve stem caps and the service port.
Use torque wrench to tighten the service port cap
to a torque of 18N.m (13.27 ft· lbs.).
Be sure to check for gas leaks.
4.6 Procedure when servicing the indoor
unit refrigeration circuit.
1. Collecting the refrigerant into the outdoor
unit
Procedure
1). Confirm that both the 2-way and 3-way valves
are set to the opened position
Remove the valve stem caps and confirm that the
valve stems are in the opened position.
Be sure to use a hexagonal wrench to operate the
valve stems.
2). Connect the charge hose with the push pin of
handle lo to the 3-way valves gas service port.
3). Air purging of the charge hose.
Open the handle Lo valve of the manifold valve
slightly to purge air from the charge hose for 5
seconds and then close it quickly.
4). Set the 2-way valve to the close position.
5). Operate the air conditioner at the cooling cycle
and stop it when the gauge indicates 0.1MPa.
6). Set the 3-way valve to the closed position
immediately
Do this quickly so that the gauge ends up indicating
0.3 to 0.5Mpa.
Disconnect the charge set and tighten the 2-way
and 3-way valve’s stem nuts.
Use a torque wrench to tighten the 3-way valves
service port cap to a torque of 18N.m.
Be sure to check for gas leakage.

Service Manual - VMH 18/28/36/48 Series
15
2. Air purging with vacuum pump
1) Completely tighten the flare nuts of the indoor
and outdoor units, confirm that both the 2-way
and 3-way valves are set to the closed
position.
2) Connect the charge hose with the push pin of
handle lo to the 3-way valves gas service
port.
3) Connect the charge hose of handle hi
connection to the vacuum pump.
4) Fully open the handle Lo of the manifold
valve.
5) Operate the vacuum pump to evacuate.
6) Make evacuation for 30 minutes and check
whether the compound meter indicates -
0.1Mpa. If the meter does not indicate -
0.1Mpa after pumping 30 minutes, it should
be pumped 20 minutes more. If the pressure
can’t achieve -0.1Mpa after pumping 50
minutes, please check if there are some
leakage points.
Fully close the handle Lo valve of the manifold
valve and stop the operation of the vacuum
pump. Confirm that the gauge needle does not
move (approximately 5 minutes after turning off
the vacuum pump).
7) Turn the flare nut of the 3-way valves about
45° counterclockwise for 6 or 7seconds after
the gas is coming out, then tighten the flare
nut again. Make sure the pressure display in
the pressure indicator is a little higher than
the atmosphere pressure. Then remove the
charge hose from the 3-way valve.
8) Fully open the 2-way valve and 3-way valve
and securely tighten the cap of the 3-way
valve.
4.7 Evacuation after servicing the outdoor
unit refrigeration circuit
1. Evacuation of the complete refrigeration
circuit, Indoor and outdoor unit.
Procedure:
1). Confirm that both the 2-way and 3-way valves
are set to the opened position.
2). Connect the vacuum pump to 3-way valve’s
service port.
3). Evacuation for approximately one hour.
Confirm that the compound meter indicates -
0.1Mpa (500 Microns / 29.9 in, hg).
4). Close the valve (Low side) on the charge set,
turn off the vacuum pump, and confirm that the
gauge needle does not move (approximately 5
minutes after turning off the vacuum pump).
5). Disconnect the charge hose from the vacuum
pump.
2. Refrigerant charging
Procedure:
1). Connect the charge hose to the charging
cylinder, open the 2-way valve and the 3-way
valve.
Connect the charge hose which you disconnected
from the vacuum pump to the valve at the bottom

Service Manual - VMH 18/28/36/48 Series
16
of the cylinder. If the refrigerant is R410A, make
the cylinder bottom up to ensure liquid charge.
2). Purge the air from the charge hose
Open the valve at the bottom of the cylinder and
press the check valve on the charge set to purge
the air (be careful of the liquid refrigerant).
3) Put the charging cylinder onto the electronic
scale and record the weight.
4). Open the valves (Low side) on the charge set
and charge the system with liquid refrigerant
If the system cannot be charge with the specified
amount of refrigerant or can be charged with a
little at a time (approximately 150g each time),
operating the air conditioner in the cooling cycle;
however, one time is not sufficient, wait
approximately 1 minute and then repeat the
procedure.
5). When the electronic scale displays the proper
weight, disconnect the charge hose from the 3-
way valve’s service port immediately
If the system has been charged with liquid
refrigerant while operating the air conditioner, turn
off the air conditioner before disconnecting the
hose.
6). Mounted the valve stem caps and the service
port. Use torque wrench to tighten the service
port cap to a torque of 18N·m (13.27 ft· lbs.).
Always leak check after servicing the refrigerant
system.
For A-VMH36QU, A-VMH48PU-1
There are one low-pressure centralized valve and
one high-pressure centralized valve, it will be
more time saving when vacuum and recycle
refrigerant. But refer to the previous instruction
when vacuum and recycle refrigerant.

Service Manual - VMH 18/28/36/48 Series
17
5. Electronic Function
5.1 Abbreviation
T1: Indoor ambient temperature
T2: Middle indoor heat exchanger coil
temperature
T2B: Indoor heat exchanger exhaust coil
temperature (located on the outdoor unit)
T3: Outdoor heat exchanger pipe temperature
T4: Outdoor ambient temperature
T5: Compressor discharge temperature
5.2 Electric Control Working Environment.
5.2.1 Input voltage: 230V.
5.2.2 Input power frequency: 60Hz.
5.2.3 Indoor fan standard working amp.: <1A
5.2.4 Outdoor fan standard working amp.: <1.5A.
5.2.5 Four-way valve standard amp.: <1A.
5.3 Main Protection
5.3.1 Compressor Restart Delay
---- The compressor takes 1 minute to start up the
first time. Further restarts take 3 minutes.
5.3.2 Temperature Protection of Compressor
Discharge.
When the discharge temperature of the
compressor rises, the running frequency is limited
according to the following rules:
----If 105℃(221 ℉) ≦T5<110℃(230 ℉),
maintain the current frequency.
----If the temperature increase and T5≧110℃
(230 ℉), decrease the frequency to a lower level
every 2 minutes till to F1.
---If T5≧115℃(239 ℉) for 10 seconds, the
compressor stops and then restart until T5<90℃
(194 ℉).
5.3.3 Fan Speed Malfunction
---- If outdoor fan speed is lower than 100RPM or
higher than 2400RPM for 60 seconds or more,
the unit stops and LED displays E8 failure code.
5.3.4 Inverter Module Protection.
---- The inverter protection module ensures that
faults related to current, voltage, or temperature
does not damage the inverter.
If these protections are triggered, the A/C unit
stops, and the LED displays the failure code.
The unit restarts 3 minutes after the protection
mechanism has turned off.
5.3.5 Low Voltage Protection
VOLTAGE
No limit
VOLT_LTM_FREQ1_ADD
VOLT_LTM_FREQ2_ADD
Note: If low voltage protection triggers and
voltage is not restored to normal within 3
minutes, the protection remains active even
after a machine restart.
5.3.6 Compressor Current Limit Protection
The temperature interval for the current limit is
the same as the range of the T4 frequency limit.

Service Manual - VMH 18/28/36/48 Series
18
Cooling mode:
Cool Return I
The difference between current limits
and shutdown current
CoolT4Zone5I
Cooling T4
≥
50
℃
current limit value
CoolT4Zone4I
Cooling 49
＞
T4
≥
45
℃
current limit
value
CoolT4Zone3I
Cooling 44
＞
T4
≥
41
℃
current limit
value
CoolT4Zone2I
Cooling 40
﹥
T4
≥
33
℃
current limit
value
CoolT4Zone1I
Cooling 32
＞
T4
℃
current limit value
Cool Stop I
Cooling stop protection current value
Heating mode:
℃
15
14 HeatT4Zone4I
10
9 HeatT4Zone3I
6
5 HeatT4Zone2I
HeatT4Zone1I
H
H
e
e
a
a
t
t
R
R
e
e
t
t
u
u
r
r
n
n
I
I
The difference between current limits
and shutdown current
H
H
e
e
a
a
t
t
T
T
4
4
Z
Z
o
o
n
n
e
e
4
4
I
I
Heating T4
≥
15
℃
current limit value
H
H
e
e
a
a
t
t
T
T
4
4
Z
Z
o
o
n
n
e
e
3
3
I
I
Heating
14
＞
T4
≥
10
℃current limit
value
H
H
e
e
a
a
t
t
T
T
4
4
Z
Z
o
o
n
n
e
e
2
2
I
I
Heating
9
＞
T4
≥
6
℃current limit
value
H
H
e
e
a
a
t
t
T
T
4
4
Z
Z
o
o
n
n
e
e
1
1
I
I
Heating
5
＞
T4
current limit value
H
H
e
e
a
a
t
t
S
S
t
t
o
o
p
p
I
I
Heating stops protection current value
5.3.7 Indoor / Outdoor Units Communication
Protection
If the indoor units do not receive the feedback
signal from the outdoor units for 2 consecutive
minutes, the unit stops. The unit displays the
failure code.
5.3.8 High Condenser Coil Temp. Protection
T3
Resume
Off
Decrease
Hold
5.3.9 Outdoor Unit Anti-Freezing Protection
When T2<4℃for 250 seconds or T2<0℃, the
indoor unit capacity demand is zero and resumes
normal operation when T2>8℃and the protection
time is no less than 3 minutes.
5.3.10 Oil Return
Rules for Operation
1. If the compressor frequency continues to be
lower than the frequency set for setting time, the
unit raises the frequency to the frequency set for
setting time and then resumes with the former
frequency.
2. The EXV continues at 300p while indoor units
maintain their operation.
If the outdoor ambient temperature is higher than
the set frequency during oil return, the unit stops
the oil return process.
℃C
C
o
o
o
o
l
l
T
T
4
4
Z
Z
o
o
n
n
e
e
5
5
I
I
50
49
45
C
C
o
o
o
o
l
l
T
T
4
4
Z
Z
o
o
n
n
e
e
4
4
I
I
44
41
40 C
C
o
o
o
o
l
l
T
T
4
4
Z
Z
o
o
n
n
e
e
3
3
I
I
33
32
C
C
o
o
o
o
l
l
T
T
4
4
Z
Z
o
o
n
n
e
e
2
2
I
I

Service Manual - VMH 18/28/36/48 Series
19
5.3.11 Low Outdoor Ambient Temperature
Protection
When the compressor is off and T4 is lower than -
35℃for 10 seconds, the unit stops and displays
“LP.”
When the compressor is on and T4 remains lower
than -40℃for 10 seconds, the unit stops and
displays “LP.”
When T4 is no lower than -32℃for 10 seconds,
the unit exits protection.
5.4 Control and Functions
5.4.1 Capacity Request Calculation
For Old Console series, Old Duct/Cassette/Floor
Ceiling, Old Vertu/Luna Series:
Total capacity Request=Σ(Norm code × HP) /10×
modify rate+ correction
For All new models (New Wall mounted (Hi-Wall)
series, New Duct/Cassette/Console/Floor Ceiling):
Total capacity Request=Σ(Norm code × HP) /40×
modify rate+ correction ∑
Cooling Mode:
T1 Ts
3
1
1
e
c
a4
2
0
2
3
0
1
f
d
b
Capacity area a b c d e f
Norm code (N)
3
2
1.5
1
0.5
0
Model
9K
12K
18K
24K
HP
1.0
1.2
1.5
2.5
Note: The final result is an integer.
Use the following table and final capacity
request to confirm the operating frequency.
Frequency (Hz) 0
COO
L_F1
COO
L_F2
…
…
COOL
_F24
COO
L_F2
5
Amendatory
capacity
demand.
0 1 2 …
…24 25
The maximum running frequency is adjusted
according to the outdoor ambient temperature
℃
55
54 Fm ax =
T4 FREM A XC 0
51.5
50.5 Fm a x = T4 FREM A X C 1
45.5
44.5 Fm a x = T4 FREM A X C 2
39
38 Fm ax = T4 FREM A X C3
33
32 Fm ax = T4 FREM A X C4
30
29 Fm ax = T4 FREM A X C5
22
20 Fm ax = T4 FREM A X C6
10
8Fm ax = T4 FREM A X C7
0
-2 Fm ax = T4 FREM A X C8
-10
-12 Fm a x= T4 FREM A X C 9
Fm ax = T4 FREM A X C1 0
Heating Mode
T1 Ts
4
0
a
3
1
-1
3
1
2
0
b
c
d
e
f
2
Capacity area a b c d e f
Norm code (N) 3 2 1.5 1 0.5 0

Service Manual - VMH 18/28/36/48 Series
20
Model
9K
12K
18K
24K
HP
1.0
1.2
1.5
2.5
Note: The final result is an integer.
Then modify it according to a T2 average
(correction):
Note: Average value of T2：Sum T2 value of all
(indoor units) / (indoor units’ number)
℃
T2 average
Decrease frequency
47
Keep frequency
40
Increase frequency
Use the following table and final capacity
request to confirm the operating frequency.
Frequency (Hz) 0 HEAT
_F1
HEAT
_F2 … HEAT
_F24
HEAT
_F25
Amendatory
capacity
demand.
0 1 2 … 24 25
The maximum running frequency is adjusted
according to the outdoor ambient temperature
℃
34
33 Standby
28
27 Fm ax= T4 FREHEA TM A X1
25
24 Fm ax= T4 FREHEA TM A X2
22
21 Fm ax= T4 FREHEA TM A X3
19
18 Fm ax= T4 FREHEA TM A X4
17
16 Fm ax= T4 FREHEA TM A X5
15
14 Fm ax= T4 FREHEA TM A X6
12
11 Fm ax= T4 FREHEA TM A X7
6
5Fm a x = T4 FREH EA TM A X 8
1
0Fm a x = T4 FREH EA TM A X 9
-3
-4 Fm ax = F2 1
-7
-8 Fm ax = F2 2
-11
-12 Fm a x = F2 3
-15
-16 Fm a x = F2 4
Fm ax = F2 5
5.4.2 Defrosting Control
Conditions for Defrosting:
After the compressor starts and enters normal
operation, mark the minimum value of T3 from
the 10th to 15th minute as T30.
If any one of the following conditions is satisfied,
the unit enters defrosting mode:
1) If the compressor’s cumulative running time
reaches 29 minutes and T3< TCDI1 and T3＋
T30SUBT3ONE≦T30.
2) If the compressor cumulative running time
reaches 35 minutes and T3< TCDI2 and T3＋
T30SUBT3TWO≦T30.
3) If the compressor cumulative running time
reaches 40 minutes and T3< -24C for 3 minutes.
4) If the compressor cumulative running time
reaches 120 minutes and T3<-15℃.