AUX air conditioner service manual
185
three- phase. Single phase motor has two windings, i.e. startup winding and running winding. There’re
3 binding posts, in shell junction box of compressor. They are marked by A, B and C individually,
representing running post, startup post and common post. R and S are series connection points of two
windings, resistance value is sum of startup and running winding resistances; between C and S is
connection point of startup winding; between C and R is connection point of running winding.
Common faults of single phase motor are winding short circuit, disconnection and shell connecting.
Check the resistance of any two of three binding posts by using Rx1 of universal meter. Resistance of
windings of most compressor shall be as follows: R
SR
= R
CS
+ R
CR
，R
CS
≥R
CR.
Among which, R
CR
stands
for running winding resistance, R
CS
stands for startup winding resistance and R
SR
stands for total
resistance of windings.
Foregoing rule doesn’t work in all totally enclosed compressors, for some compressors, R
CS
≥R
CR,
for
some compressors, R
CS
= R
CR.
For some compressor, main winding and assistant winding can not be
judged according to normal rules because of different ways of wiring. Therefore, wire shall be
connected correctly as per connection diagram provided by manufacturer.
(1)Short circuit inspection for motor windings
Short circuits of windings refer to the fact that insulation performance of winding has been disrupted
which cause short circuit, including inter-turn short circuit, winding burnout, inter-winding and
inter-phase short circuit.
In some cases of short circuit, motor still runs, but runs slowly and current is excess large. Contrast
value of velocity /current depends on how many windings have short circuited. Remove outside wire
of motor, check resistance between C and S, and resistance between C and R, if resistance of terminal
of certain winding is lower than normal value, it shows that this winding has short circuited.
(2)Broken-circuit inspection of motor winding
Connection lugs in junction box are not welded or locked firmly and loose or break during operation.
In addition, insulation wires don’t insulate properly, and winding burns out. The motor can’t be run
because of broken-circuit.
Remove outside wire of motor, check conduct condition of two connection points with R×1 of
universal meter. If two connection terminals don’t conduct, i.e. resistance between them is infinite
large, undoubtedly, this winding has broken. Find out broken points and connect them again.
(3)Grounding inspection of motor windings
Motor windings being affected by moisture, insulation layer aging or being damaged and other
condition may cause short circuit of motor windings and shell. Under such circumstance, motor can
not start up and fuse will burn out or relay will trap. Check the winding with universal or megohm
meter, with one handle touching common terminal and the other handle touching motor shell. If
resistance is very low, windings touch the shell and cause short circuit. While checking, remove a scar
on the motor shell and touch the bare metal for measure.
There’re two connection forms for windings of three phase motor: star(Y )type and triangle ( ) type. △
Resistance values of three windings are same in both cases. Winding short circuit, breakout circuit and
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