Hitachi RAS-E10H2 - Temperature Detection Circuit Details

Main P.W.B.
HIC
O.H. thermistor
DEF. thermistor
Outdoor temperature
thermistor
Microcomputer
AX-8V10
OH
DEF
Outdoor
temperature
59
63
64
0V
0V
0V
C302
0V
R303
R306
0V
R302
R305
C303
C304
R304
R301
0V
CN8
CN9
+5V
+5V
+5V
CN10
1
2
1
2
1
2
Outdoor temperature
(
℃
)
−
10
1.19
0
1.69
10
2.23
20
2.75
30
3.22
40
3.62
20
21
22
6-4.
Te
mperature Detection Circuit
The
Ov
er
heat
ther
mistor
circuit
detects
the
temperature
at
the
surf
ace
of
the
compressor
head,
the
Defrost.
ther
mistor circuit detects the defrosting operation temperature
.
A
ther
mistor
is
a
negativ
e
negative negativ
resistor
element
which
has
the
character
istics
that
the
higher
(lo
w
er)
the
temperature
,
the lo
w
er (higher) the resistance
.
When the compressor is heated, the resistance of the Over heat thermistor becomes low and voltage to
a
pin
59
59
of microcomputer is increased.
of microcomputer is increased.
microcomputer judges that the compressor is overheated and stops operation.
When
frost
fo
r
ms
on
the
outdoor
heat
e
xchanger
,
the
temperature
at
the
e
xchanger
drops
abr
uptly
.
uptly. uptly
Theref
ore
ThereforeTheref
If this v
oltage becomes lo
If this voltage becomes loIf this v
w
er than the set v
alue stored inside
, the microcomputer star
ts defrosting control.
Dur
ing
defrosting
operation
the
microcomputer
tr
ansf
ers
the
defrosting
condition
command
to
the
indoor
microcomputer via the circuit interf
ace
.
tr
ansf
ers
it
to
the
indoor
unit,
thus
controlling
the
compressor
rotation
speed
according
to
the
v
alue
set
at
the
EEPR
OM
in
the
indoor
unit,
and
s
witching
switching s
the
operation
status
(outdoor
f
an
on/off
,
etc.)
in
the
dehumidifying
mode.
The f
ollo
The folloThe f
wing sho
ws the typical v
alues of outdoor temperature in relation to the v
oltage:
alues of outdoor temperature in relation to the voltage:alues of outdoor temperature in relation to the v
<Ref
erence>
appro
x.
0V
;
when the ther
mistor is shor
ted, the
y are appro
x.
5
V
, and LD301 b
V, and LD301 bV
links se
ve
n times
.
Ho
we
ve
r,
an
error
is
detected
only
when
the
OH
ther
mistor
is
shor
ted;
in
such
a
case
,
the
b
linking
mode
is entered 12 minutes after the compressor star
ts oper
ation.
Fig. 6-12
R303 Voltage (V)
Microcomputer compares the voltage at pin
59
with the internal set value, if it is exceeded the set value
with the internal set value, if it is exceeded the set value
the resistance of the Defrost. thermistor becomes high and the voltage at pin
63
of microcomputer drops.
of microcomputer drops.
The microcomputer always reads the outdoor temperature via a thermistor (microcomputer pin
64
), an
), an
Table 6-2
When the thermistor is open, in open status, or is disconnected, microcomputer pins
59 ,
63 ,
64
are
ⅠC2
6-5. Reversing valve control circuit
●
In this unit, reversing valve control circuit turns ON/OFF the power to the reversing valve coil by
opening/closing the reversing valve relay
.
●
Opening/closing of relay will differ depending on the operation condition. (In the cooling cycle,
reversing valve relay is normally ON (close).)
●
Table 6-3 shows the circuit operation of each operation mode. If the following result is not obtained,
reversing valve control circuit may be defective.
Table 6-3
Point
Operation mode
Cooling
In normal cooling operation
In normal heating operation
In defrosting operation
approx. 35 V
approx. 35 V
0VHi
0VHi
12VLo 0V (not fixed)
Heating
Between Pin 29
of microcomputer and 0V
Between Pin 32 of HIC
and 0V
Between 1 and 3 CN2
Main P.W.B.
Reversing
valve
Reversing valve
relay coil
(RL5)
HIC
Fig. 6-13
Microcomputer
Reversing valve relay
RL5
- 62
-