12KHR-N
3 – 13
3. Caution in checking printed circuit boards (PWB)
3.1. Non-insulated control circuit
The GND terminals of the low-voltage circuits (control circuits for microcomputer and thermistors and drive circuits for expansion valve and relays) on
the control printed circuit board (PWB) are connected to the compressor drive power supply (320-VDC negative terminal). Therefore, exercise utmost
caution to prevent electric shock.
If a measuring instrument used for the test is grounded, its chassis (ground) has the same electric potential as the 0-V probe. Since non-insulated cir-
cuits have the following voltage potential difference from the ground, connection of the grounding wire results in a short-circuit between the 0-V line
and the ground, thus allowing an excessive current to flow to the tester to cause damage.
If the sheaths of the thermistor lead wires or expansion valve lead wires inside the outdoor unit become damaged due to pinching by the front panel
or other metal parts or contacting a pipe, a high voltage can flow and destroy the circuits. To prevent these problems, carefully conduct assembly
work.
Terminal board
Ground
0-V line
Point (F)
Point (E)
Reactor
IPM
+
-
Compressor motor
2
AC230V
1
N
Outdoor unit circuits
M
Reason
The oscilloscope (chassis ground) has the same electric potential as the 0-V probe. The
entire electronic control section of the outdoor unit has a voltage potential difference from
the ground as shown in the above diagram. When the oscilloscope is set up, the 0-V line
and the ground voltage (ground) will be short-circuited, resulting in an excessive current
flow to cause damage to the oscilloscope or indoor electric circuits.
Do not touch the
cabinet or bring metal
parts into contact with
the cabinet.
Danger!!
Do not connect
the grounding
wire.
