Mitsubishi Electric MXZ-SM72TAM-U1 Service Manual page 42

1500 (U7): Superheat due to low discharge temperature trouble
Abnormal points and detection methods
10 or more minutes after the compressor starts operation,
if a discharge superheat of -27°F (-15°C)* or less is detect-
ed for 5 consecutive minutes even though the indoor LEV
has the minimum open pulse.
LEV:
Linear expansion valve
TH4:
Thermistor <Compressor>
63HS:
High pressure sensor
* At this temperature, conditions for the abnormality detection
will not be satisfied if no abnormality is detected on either TH4 or 63HS.
Diagnosis of failure
Is the TH4 wiring disconnected?
Check the resistance of TH4.
Is the resistance normal?
Check the connector contact and wiring of the
indoor LEV.
Is there any abnormality such as
half-disconnection or breakage?
Disconnect the indoor LEV wiring to check the
resistance.
Continue to the next page.
OCH800A_42
Yes
(Disconnected)
No
(Connected properly)
No
Yes
Yes
No
Causes and checkpoints
• Disconnection or loose connection of TH4
• Defective holder of TH4
• Disconnection of LEV coil
• Disconnection of LEV connector
• LEV performance failure
Connect the wiring properly.
temp. - resistance characteristic
32°F (0°C) 700 kΩ
50°F (10°C) 410 kΩ
68°F (20°C) 250 kΩ
86°F (30°C) 160 kΩ
104°F (40°C) 104 kΩ
Replace the TH4.
Connect the connector properly, or replace the
LEV.
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