Hitachi RAS-25CNH2 Service Manual page 51

5. Reversing valve control circuit
Reversing
valve
V
DC voltmeter
or tester
❈
Since the reversing valve is differential pressure system, even when reversing valve is ON (collector
voltage of Q701 is about 0.8V normally), compressor rotation speed instructed by indoor microcomputer
exceeds 3300min -
36V.
This does not indicate trouble. When rotation speed is reduced under 2700min -
will fall to about 0.8V again. To measure voltage, connect Œ terminal of tester to D701 anode and œ
terminal to D line on the terminal board.
By reversing valve control circuit you can switch reversing valve ON/OFF according to instruction from
G
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
3
D701
1
Q701
I/F 0V
1
, signal at pin 5 of microcomputer changes, and collector voltage of Q701 will be about
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 36V
12V
PQ701
R705 R233
R706
Fig. 5 — 1
Table 5-1
Collector voltage of Q701
– 54 –
8J-HIC
56 5
MICRO
COMPUTER
1
, collector voltage of Q701
About 36V
About 0.8V
About 0.8V
About 36V
About 36V