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25

2-3 Overcurrent protection
(1) Compressor lock detection

If the set value (4.25 A) of AC current is exceeded at 17 to 30 Hz when operation begins, operation is stopped. In this
case, the compressor outdoor fan does not stop, and 170 seconds after operation is stopped, another try will be made.
Three retries are allowed. On the fourth retry, a complete stop request signal is sent to the indoor unit, and the outdoor
unit will remain stopped until reset is performed. At this time, the 3-minute delay for control of the outdoor unit will not
function; therefore, do not cancel by removing the plug and cutting the power.

(2) DC overcurrent detection, AC overcurrent detection

To protect against overcurrent due to sudden changes in load, the compressor is stopped if the set value 30 A DC is
exceeded in the DC section, or the set value 15 A AC is exceeded in the AC section. In this case, the outdoor fan does
not stop, and 170 seconds after operation is stopped, another try will be made. Three retries are allowed. On the fourth
retry, a complete stop request signal is sent to the indoor unit, and the outdoor unit will remain stopped until reset is
performed. At this time, the 3-minute delay for control of the outdoor unit will not function; therefore, do not cancel by
removing the plug and cutting the power.

If the temperature of the compressor chamber exceeds 114

°

C, the compressor is stopped. In this case, the outdoor fan

does not stop, and when the compressor chamber temperature decreases to 100

°

C three minutes after operation is

stopped, another try will be made. Three retries are allowed. On the fourth retry, a complete stop request signal is sent
to the indoor unit, and the outdoor unit will remain stopped until reset is performed. At this time, the 3-minute delay for
control of the outdoor unit will not function; therefore, do not cancel by removing the plug and cutting the power.

If the temperature of the chips in the power transistor module exceeds 105 

°

C, the compressor is stopped. In this case,

the outdoor fan does not stop, and when the temperature of the chips in the power transistor module decreases to 105

°

C  170 seconds after operation is stopped, another try will be made. Three retries are allowed. On the fourth retry, a

complete stop request signal is sent to the indoor unit, and the outdoor unit will remain stopped until reset is performed.
At this time, the 3-minute delay for control of the outdoor unit will not function; therefore, do not cancel by removing the
plug and cutting the power.

2-6 Serial signals
(1) Serial signals consist of all 96-bit signals.
(2) If the outdoor unit does not receive a serial signal, it will stop approximately 30 seconds later. Note that this is true only

of normal operation; in test mode, it does not stop and operation takes place based on the test mode commands.

26

Function

NO

Description

Detection 

time

Restart 

condition

Restart 

times

Indoor Outdoor

Operation

Self diagnostic

display

1

2

3

4

5

6

Indoor fan 
lock

Indoor fan 
rpm error

Indoor 
freezing 
guard

Indoor 
overheating 
control

DC 
overcurrent
or overheat of 
the IPM

AC 
overcurrent

Compressor 
lock

Stops operation if no revolution pulse 
signal is input from the indoor fan motor for 
one minute.

Stops operation if the revolution pulse 
signal from the indoor fan indicates low 
rpm (approximately 300 rpm or less).

Lowers the operating frequency if the 
temperature of the indoor heat exchanger 
goes below 5

°

C during cooling. Stops the 

compressor if the temperature stays below 
0

°

C for 4 minutes.

Lowers the operating frequency if the 
temperature of the indoor heat exchanger 
rises above the overheating temperature 
during heating. Stops the compressor if the 
temperature stays above the overheating 
temperature for 1 minute at minimum 
frequency.
Set values for overheating temperature

During normal operation: 51

°

C to 54

°

C

During full power operation: 54

°

C to 

58

°

C

Stops the compressor if a current of 
approximately 30 A or more flows in the 
power transistor module. Also stops the 
compressor if the temperature of the 
power transistor module is exceeds 105

°

C.

Lowers the operating frequency if the 
compressor AC current exceeds 
Peak control level 
[11.3A(heating), 10.4A(cooling)] 
Stops the compressor if the current 
exceeds peak control level at 40 Hz or less.
Stops the compressor if the compressor 
AC current exceeds 15 A.

Stops the compressor if the compressor 
AC current exceeds 4.25 A immediately 
after activating the compressor (at 17 to 30 
Hz).

When indoor 
fan is revolving

During cooling 
and dry 

During heating

During 
compressor 
operation

During 
compressor 
operation

Immediately 
after 
compressor 
activation.

Operation OFF

Automatically 
restarts when the 
exchange 
temperature rises 
above the freezing 
prevention 
temperature (above 
2

°

C)

Automatically 
restarts when the 
exchange 
temperature goes 
below the 
overheating 
temperature.

Automatically 
restarts after safety 
time (170 seconds) 

Automatically 
restarts after safety 
time (170 seconds)

Automatically 
restarts after safety 
time (170 seconds) 

No limit

No limit

No limit

4 times

4 times

4 times

Yes

No

No

Yes

Yes

Yes

No

No

No

Yes

Yes

Yes

 

  

27

Compressor 
overheating 
control

Compressor 
high 
temperature 
error

Outdoor 
overheating 
control

Outdoor 
thermistor 
short

Outdoor 
thermistor 
open

AC abnormal 
current error

Serial signal 
error

Lowers the operating frequency if the 
temperature of the compressor chamber 
thermistor (TH1) rises above 105 

~

107

°

C.

Stops the compressor if the thermistor 
stays above 104 

~

 106

°

C for 4 minutes, 

or 1 minute at minimum frequency or less.

Stops the compressor if the compressor 
chamber thermistor is above 114

°

C.

(Or when TH1 shorts)

Lowers the operating frequency if the 
temperature of the outdoor heat exchanger 
rises above 57

°

C during cooling. Stops the 

compressor if the temperature stays above 
57

°

C for 4 minutes, or 1 minute at 

minimum frequency or less.

Stops the compressor if an outdoor 
thermistor (excluding TH1) shorts.
(Except for the AU-X127E)

Stops the compressor if the circuit of an 
outdoor thermistor breaks.
(Except for the AU-X127E)

Stops the compressor if if the operating 
frequency is above 70 Hz and the 
compressor current is below 1.0 A.

Turns the compressor relay off if the indoor 
unit does not receive a serial signal from 
the outdoor unit for 8 minutes.

Stops the compressor if the outdoor unit 
does not receive a serial signal from the 
indoor unit for 30 seconds.

During 
compressor 
operation

During 
operation

During 
compressor 
operation

When 
compressor is 
activated

When 
compressor is 
activated

During 
compressor 
operation

During 
operation

During 
operation

Automatically 
restarts after safety 
time (170 seconds)

Automatically 
restarts when 
thermistor (TH1) 
temperature falls 
below 100

°

C 

(approximately 30 
minutes)

Automatically 
restarts after safety 
time ( (170 seconds)

Automatically 
restarts after safety 
time  (170 seconds)

Automatically 
restarts after safety 
time  (170 seconds)

Automatically 
restarts after safety 
time  (170 seconds)

Automatically 
restarts less than 8 
minutes after 
operation stops

Restarts after 
reception of serial 
signal

No limit

4 times

No limit

4 times

4 times

4 times

No limit

No limit

No

Yes

No

Yes

Yes

Yes

Yes

No

Yes

No

Yes

Yes

Yes

Yes

28