80
Frequency drop by current
protection
When the outdoor unit input current exceeds 22.5 A, the compressor
operates at reduced frequency.
These symptoms do not mean any
abnormality of the product, but check the
following points.
• Air filter clogging.
• Amount of gas.
• Short cycle of indoor/outdoor air flow.
Display
Abnormal
Detecting method
Check points
Symptom
Outdoor unit operates. (The compressor operates at reduced frequency.)
Frequency drop by overload
protection
When the compressor load exceeds the specified value, the compres-
sor operates at reduced frequency.
Frequency drop by high pres-
sure protection
When indoor pipe temperature exceeds 131°F during heating, the com-
pressor operates at reduced frequency.
Frequency drop by defrosting
in cooling
When the indoor pipe temperature falls to 42.8°F or below during cool-
ing, the compressor operates at reduced frequency.
Frequency drop by discharge
temperature protection
When the discharge temperature exceeds 230°F, the compressor oper-
ates at reduced frequency.
Frequency drop by high pres-
sure switch (63H1) protection
When the high pressure exceeds 398 PSIG, the compressor operates
at reduced frequency. In addition, the fan speed changes.
• Amount of gas.
• Outdoor unit air passage.
Low discharge temperature
protection
When the state with low discharge temperature of which 122°F in COOL
and 119.3°F or less in HEAT for 20 minutes, the compressor operates
continuously.
Check the amount of gas.
• Replace the outdoor controller board.
• Check the contact of LEV board connec-
tors.
Defrost thermistor abnormality
When a short or open circuit occurs in the defrost thermistor during
heating
* In this case, the compressor continues to operate.
• Defrost thermistor characteristic.
• Contact of P. C. board connectors.
Display
Abnormal
Detecting method
Check points
Symptom
Outdoor unit operates.
Power factor detection abnor-
mality
When the compressor power factor cannot be detected
* In this case, the compressor keeps running.
• Compressor wiring.
d
d8
8
(d8)
d
d9
9
(d9)
d
d77
(d7)
d
d6
6
(d6)
d
d3
3
(d3)
d
d11
(d1)
e
e77
(E7)
h
h44
(h4)
Room
temperature
thermistor(RT11)
Part name
Check method and criterion
Measure the resistance with a tester. (Part temperature 50°F ~ 86°F)
Figure
Normal
8k
Ω
~ 20k
Ω
Abnormal
Open or short-circuit
Indoor coil
thermistor(RT12)
2. Trouble criterion of main parts
MSH09TW
MSH12TN
MSH15TN
MSH17TN
MSH09TW -
MSH12TN -
MSH15TN -
MSH17TN -
U1
U1
U1
U1
MUH09TW
MUH12TN
MUH15TN
MUH17TN
MUH09TW -
MUH12TN -
MUH15TN -
MUH17TN -
U1
U1
U1
U1
Defrost
thermistor(RT61)
Measure the resistance with a tester.
(Part temperature 14°F ~ 104°F)
Normal
5k
Ω
~ 60k
Ω
Abnormal
Open or short-circuit
Ambient temper-
ature thermistor
(RT63)
MSH09TW -
MSH12/15/17TN -
only
U1
U1
Measure the resistance between the terminals with a tester.
(Part temperature14°F ~ 104°F)
Compressor(MC)
MUH09TW
MUH12/15/17TN
OPEN 302°F
i
9°F
CLOSE
203°F
i
18°F
P
RED
BLK
WHT
Normal
0.7~0.9
Ω
1.3~1.6
Ω
1.4~1.9
Ω
MUH12/15
C-R
C-S
Abnormal
Open or
short-circuit
2.4~3.0
Ω
1.4~1.8
Ω
2.3~2.9
Ω
MUH17
MUH09
MUH12TN -
MUH15TN -
U2
U2
OB275--3.qxp 03.12.2 5:19 PM Page 80
Summary of Contents for MSH09TW
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