Thermistor; Thermistors For The Outdoor Unit; Thermistor For Upper Part Temperature Of Compressor - Hitachi RAS-(3-6)HVRNM2E Service Manual

11 Electrical checks of
main parts

11.2 Thermistor

Thermistors for the outdoor unit

1. Thermistor for discharge gas temperature (THM9).
2. Thermistor for outdoor ambient temperature (THM7).
3. Thermistor for evaporating temperature (THM8).

Thermistor for upper part temperature of compressor

(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 lubricating
oil deterioration occurs and lubricating properties deteriorate
resulting in short compressor life.
2 If discharge gas temperature increases excessively compres-
sor temperature increases. At the worst compressor motor
winding will be burnt out.
3 When the upper part temperature of compressor increases du-
ring heating operation the unit is controlled 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 decreasing compressor tempe-
rature.
• If the compressor upper part temperature increases ex-
ceeding 132 ºC 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.
4 If compressor upper part temperature increases excessively
the protection control is activated and the compressor is
stopped according to the following method.
451
SMGB0064 rev.0 - 08/2011
200
200
R25 = 200k
B = 3920k
100
72.3
14.2
0
25 30 100
Temperature (°C)
Resistance Characteristics of Thermistor
for discharge Gas Overheating Protection
5.3
132 150
11