Hitachi RAS-50WX8 Service Manual page 90

5. Reversing valve control circuit
Reversing
valve
DC voltmeter
V
or tester
Since the reversing valve is differential pressure system, even when reversing valve is ON (collector valtage of Q701 is
about 0.8V nomally), compressor rotation speed instructed by indoor microcomputer exceeds 3300min
microcomputer changes, and collector voltage of Q701 will be about 36V.
This does not indicate trouble. When rotation speed is reduced under 2700min
0.8V again. To measure voltage, connect + terminal of tester to D702 anode and - terminal to D line on the terminal
board.
By reversing valve control circuit you can switch reversing valve ON/OFF according to instruction from indoor
microcomputer and depending on operation condition.
Voltage at each point in each operation condition is approximately as shown below when measured by tester.
(When collector voltage of Q701 is measured)
Cooling
Heating
Dehumidifying
CN2
FUSE RESISTOR
3
D702
1
Q701
R701
R702
I/F 0V
Operation condition
General operation of Cooling
In normal heating operation
MAX. rotation speed instructed
by indoor microcomputer after
defrost is completed
Defrosting
SENSOR DRY
I/F 35V
5V
PQ701
R703
0V
Fig. 5-1
-1
, collector voltage of Q701 will fall to about
Table 5-1
Collector voltage of Q701
– 130 –
HIC
R219
MICROCOMPUTER
24
16
Q705
-1
, signal at pin
About 35V
About 0.8V
About 0.8V
About 35V
About 35V
of