Mitsubishi Electric MS-A WA, Service Technical Manual

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24
In COOL mode, the two indoor coil thermistors (one main and one sub) sense temperature ununiformity (super heat) at the
heat exchanger, and when temperature difference develops, the indoor coil thermistors adjust LEV opening to diminish the
super heat. This action is called Evaporation Temperature Protection.
Indoor heat
exchanger
(MXZ-3A30NA)
Outdoor
heat
exchanger
Exclusive
LEV
Receiver
LEV
Receiver
The opening pulse of the Receiver LEV is fixed to the standard No.3 in cooling operation, and so is that of each Exclusive
LEV in heating operation.
However the opening pulse will be changed to the standard No.4 or No.5 when the discharge temperature protection or high-
pressure protection is working.
In addition to that, it will also be changed to standard No.2 or No.1 when the opening pulse of the each Exclusive LEV
becomes 100 pulse or less in cooling operation or so does that of Receiver LEV in heating operation.
MXZ-2A20NA/3A30NA
The table below shows the role of Exclusive LEV and Receiver LEV in each operation mode.
Circulation Amount
Control
Capacity Distribution
Discharge
Temperature
Protection
High Pressure
Protection
Evaporation
Temperature
Protection
COOL
Exclusive LEV
○ ○ ○ ○ ○
Receiver LEV
× × ○ ○ ○
HEAT
Exclusive LEV
× ○ ○ ○
—
Receiver LEV
○ × ○ ○
—
<MXZ-2A20NA>
Number of
operating
indoor units
Standard No.
LEV opening (pulse)
COOL HEAT
1 unit 2 units 1 unit 2 units
1 200 150 120 120
2 300 320 140 140
3 400 360 160 160
4 450 410 220 220
5 500 500 280 280
<MXZ-3A30NA>
Number of
operating
indoor units
Standard No.
LEV opening (pulse)
COOL HEAT
1 unit 2 units 3 units 1 unit 2 units 3 units
1 150 250 250 250 250 250
2 250 320 320 300 300 300
3 350 360 370 450 380 380
4 400 410 420 460 400 390
5 450 460 470 470 450 440