Check Method (Outdoor); Non-Insulated Control Circuit - Sharp AE-XM24HR Service Manual

Multi split type room air conditioners

Table of Contents

CHECK METHOD (OUTDOOR)

CAUTION IN CHECKING PRINTED CIRCUIT BOARDS (PWB)

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 (370-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.

Do not touch the

cabinet or bring metal

parts into contact with

the cabinet.

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