(Main Parts)
MAINTENANCE
4-94
SM-18006
(2) Thermistor for Upper Side of Compressor (Discharge Gas) Temperature “Td1, Td2” (THM8, 9)
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. Then the lubricating properties deteriorate, resulting in short compressor life.
b. If discharge gas temperature increases excessively, compressor temperature increases. At the
worst, compressor motor winding is burnt out.
c. When the upper part temperature of the compressor increases during heating operation, the unit is
controlled according to the following method.
• An electronic expansion valve of water source units is opened to return the liquid refrigerant to
the compressor through the accumulator, decreasing compressor temperature.
• If the compressor upper part temperature exceeds 270
o
F (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.
d. If upper part temperature of the compressor increases excessively, the protection control is
activated, and the compressor is stopped according to the following method.
Operation
Upper Part Temperature
of Compressor
Detecting Period
Cooling Over 270
o
F (132
o
C) 10 minutes (Continuously)
Over 284
o
F (140
o
C) 5 seconds (Continuously)
Heating Over 270
o
F (132
o
C) 10 minutes (Continuously)
Over 284
o
F (140
o
C) 5 seconds (Continuously)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
50
100
150
200
250
Output Voltage [VDC]
Ambient Temperature T [ºF (ºC)]
Thermistor Characteristics
Thermistor Resistance R
T
116.5kΩ
41.4kΩ
17.2kΩ
8.1kΩ
1.4V
2.7V
3.7V
4.3V
0
(-18)
50
(10)
100
(38)
150
(66)
200
(93)
250
(121)
300
(149)
R
25
= 200kΩ
(When T = 77ºF (25ºC), RT = 200kΩ
B = 3920K
R
T
= R
25
• exp B(1/T[K] - 1-298)
Thermistor Resistance [kΩ] Output Voltage [VDC]
The thermistor resistance characteristics are shown in the gure below.
To Next Page