Table of Contents
Advertisement
10. Temperature Detection Circuit
Compressor head surface temperature is detected by OH thermistor circuit, defrost operation temperature
G
is detected by DEF thermistor circuit, and outdoor temperature is detected by outdoor temperature thermistor
circuit.
Thermistor is a negative resistance element with the following characteristic: Resistance falls when
G
temperature rises, and increases when temperature falls.
When compressor is over-heated, resistance of OH thermistor decreases and voltage at pin
G
microcomputer rises.
Voltage at pin
G
x
microcomputer judges over-heating and stops operation.
If outdoor heat exchanger is frosted, heat exchanger temperature will rapidly drop. In response, resistance
G
of DEF thermistor increases and voltage at pin
set value, microcomputer enters defrost control mode.
During defrost operation, microcomputer transfers indoor unit defrost condition command from IF transmission
G
output at SDO pin of interface (pin
Outdoor temperature is always read in (voltage at pin
G
thermistor, and then transferred to indoor unit side. According to this value, compressor rotation speed
control and operation selection (outdoor fan ON/OFF, etc.) in dehumidifying mode are performed.
Represented value of the relationship between outdoor temperature and voltage are shown below.
Table 10-1
Outdoor temperature (°C)
Voltage at pin
<Reference>
When the thermistor is open or heat is shut off, pins
thermistor is short-circuited, pins
However, OH thermistor detects only short-circuit as error: It will enter a blink mode after 12 minutes or more
has elapsed from the start of compressor operation.
of microcomputer is compared with set value stored inside: If voltage exceeds set value,
and
/
of CN7 (V)
1
to
of microcomputer are set to about 5V, and LD301 blinks 7 times.
x
v
Fig. 10-1
of microcomputer falls. When the voltage falls under the
c
of microcomputer).
X
of microcomputer) by outdoor temperature
v
-10
0
10
1.19
1.69
2.23
to
of microcomputer are set to about 0 V; when
x
v
– 60 –
20
30
40
2.75
3.22
3.62
of
x
Hide quick links:
Advertisement
Table of Contents
Troubleshooting
