11 Electrical checks of
main parts
460
SMGB0087 rev.0 - 12/2013
Thermistor for discharge gas temperature (THM9)
(For prevention of discharge gas overheating)
1 A thermistor for the upper part temperature of the
compressor is installed to prevent discharge gas
from overheating.
If discharge gas temperature increases excessively lubri-
cating oil deterioration occurs and lubricating properties
deteriorate resulting in short compressor life.
2 If discharge gas temperature increases excessively
compressor temperature increases. At the worst
compressor motor winding will be burnt out.
3 When the upper part temperature of compressor in-
creases during heating operation the unit is contro-
lled according to the following method.
• An electronic expansion valve of outdoor units
is (are) opened to return the liquid refrigerant
to the compressor through the accumulator de-
creasing compressor temperature.
• If the compressor upper part temperature in-
creases exceeding 132 ºC even if an electro-
nic expansion valve opens the compressor
is stopped in order to protect the compressor.
In cooling operation the above function is also
available.
4 If compressor upper part temperature increases
excessively the protection control is activated and
the compressor is stopped according to the following
method.
7,47
5,76
9.93
13.4
35.1
72.3
18.7
25.1
49.9
Thermistor resistance characteristics
Temperature (ºC)
Thermistor resistance (kΩ)
Operation Upper part temperature of compressor Defecting period
Cooling
Over 132 ºC 10 minutes (continuously)
Over 140 ºC 5 seconds (continuously)
Heating
Over 132 ºC 10 minutes (continuously)
Over 140 ºC 5 seconds (continuously)
Defrosting Over 132 ºC 5 seconds (continuously)
Thermistor for outdoor ambient temperature (THM7)
The thermistor resistance characteristics are shown in the gure.
80
70
60
50
40
30
20
10
0
-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60
26.0
20.2
15.9
12.6
10.0
8.05
5.31
3.60
2.49
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