Hitachi Utopia PAS-3HVRG, Service Manual

Page: 99 / 127

3-10
MAIN PARTS
3.5.2 Thermistor for Outdoor Unit
(1) Position of Thermistor
(2) Thermistor for Upper Part Temperature of
Compressor
(For Prevention of Discharge Gas Overheating)
a. A thermistor for the upper part temperature
of the compressor is installed to prevent
discharge gas from overheating.
If discharge gas temperature increases
excessively lubricating oil deterioration
occurs and lubricating properties deteriorate,
resulting in short compressor life.
b. If discharge gas temperature increases
excessively, compressor temperature
increases. At the worst, compressor motor
winding will be burnt out.
c. When the upper part temperature of
compressor increases during heating
operation, the unit is controlled according to
the following method.
An electronic expansion valve of indoor units and high pressure refrigerant is returned to the
compressor through the accumulator, decreasing compressor temperature.
If the compressor upper part temperature increases exceeding 132 o C even if an electronic
expansion valve opens, the compressor is stopped, in order to protect the compressor.
In cooling operation, the above function is also available.
200
100
25 30 132 150
72.3
14.2
100
200
5.3
Resistance V
alue
of
Ther
mistor (k
Ω
)
Temperature (
o
C)
Resistance Characteristics of Thermistor
for Discharge Gas Overheating Protection
R25 = 200k
Ω
B = 3920k
0
Thermistor for
Evaporating
Temperature
Thermistor for
Outdoor Ambient
Temperature
Thermistor for
Discharge Gas
Temperature