Hitachi RAM-55QH4, Service Manual, Page: 83 / 109

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Table 10-1 Name and Role of each thermistor
Table 10-2 Correspondence between each thermistor's
resistance and temperature (reference value)
Electric expansion valve
thermistor
DEF thermistor
-15˚C 12.6k
Ω
1.0V
1.7V
3.0V
3.9V
1.0V
1.7V
2.4V
3.1V
4.4V
0.5V
1.3V
2.4V
3.4V
3.6V
3.9V
6.1k
Ω
2.2k
Ω
860
Ω
400
Ω
0˚C
25˚C
50˚C
75˚C
Outdoor temperature
thermistor
Temperature
25˚C
50˚C
75˚C
100˚C
105˚C
118˚C
Temperature
-15˚C
0˚C
15˚C
30˚C
Temperature
Resistance
33.9k
Ω
10.8k
Ω
4.1k
Ω
1.7k
Ω
1.5k
Ω
1k
Ω
Resistance
12.6k
Ω
6.1k
Ω
3.2k
Ω
2k
Ω
Resistance Potential
Potential
Microcomputer
pin potential
OH thermistor
Name
OH thermistor Compressor head
If the temperature of the compressor
rises abnormally (118˚C), the
compressor will be stopped. The
temperature is used to decide the
operation of the valve.
The thermistors decide the defrost
operation during heating combined
the data of the outside temperature
and its data.
The thermistors detect the
temperatures of the piping to the
indoor units. The temperatures are
used to decide how much the
expansion valve is opened.
Outdoor temperature is used to
decide the various operations of the
air conditioner.
C N 5
DEF thermistor Heat exchanger C N 6
Outdoor temperature
thermistor Outside temperature C N 7
Electric expansion valve
thermistor (NARROW PIPE 1) Indoor unit 1 (NARROW PIPE)
Electric expansion valve
thermistor (NARROW PIPE 2) Indoor unit 2 (NARROW PIPE)
Electric expansion valve
thermistor (NARROW PIPE 3) Indoor unit 3 (NARROW PIPE)
C N 8
Electric expansion valve
thermistor (WIDE PIPE 1) Indoor unit 1 (WIDE PIPE)
Electric expansion valve
thermistor (WIDE PIPE 2) Indoor unit 2 (WIDE PIPE)
Electric expansion valve
thermistor (WIDE PIPE 3) *
"
*
" mark is for model RAM-65QH4 only.
Remark :
*
Table 10-2 shows the correspondence between
the thermistor's resistance and the temperature.
They should be used as reference values. The
value, which you measure, may be slightly
difference from that in the table. It depends on
the instrument.
Indoor unit 3 (WIDE PIPE)
C N 9
Connector No Measuring Point Role
When you measure the resistance, pull out the
connector after turning off the power supply.
Pulling out the connector while the power supply
is turned on will cause troubles.