Reversing Valve Control Circuit - Hitachi RAS-25CNH1 Service Manual

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
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
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
0
£
D 701
0
1
0
Q 701
0
0
I/F 0V
1
, signal at pin of microcomputer changes, and collector voltage of Q701 will be about
24
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
12V
R 233
0
PQ 701
R 705
0
R 706
Fig. 5 - 1
Table 5-1
Collector voltage of Q701
– 73 –
HIC
8E21
§ ¤
1
, collector voltage of Q701
About 36V
About 0.8V
About 0.8V
About 35V
About 35V