A LOOK AT SERVICE SAFETY
Servicing
47
IV.
Identifying Compressor
Electrical Problems
This section describes procedures for checking the
compressor’s electrical circuits and components.
Before doing so, follow the original equipment
manufacturer’s service information (OEM) to make
sure the system is getting proper voltage and that the
control, thermostat, and contactor are working
properly. If you are servicing a water-utilizing sys-
tem, see “Servicing or Troubleshooting Water-Utiliz-
ing Systems: Preventing Explosions” on page 39.
Whenever you suspect that there is an electrical
problem with the compressor (for example, there
has been a tripped circuit breaker):
•
FIRST, check for a ground fault (also known as
a short circuit to ground) in the motor using a
megohmmeter (“megger”) or a Hi-Potential
Ground Tester (“Hi-Pot”) (Section A).
•
SECOND, check the motor windings for
proper continuity and resistance (Section B).
•
THIRD, check the compressor’s electrical
components (Sections C and D).
When checking for electrical problems, it is impor-
tant to follow all safety precautions (see warning
below) and use the proper equipment and proce-
dures.
Oil and refrigerant can spray out of the compres-
sor if one of the terminal pins is ejected from the
hermetic terminal. This can occur as a result of a
ground fault in the compressor. The oil and refrig-
erant spray can be ignited by electricity and pro-
duce flames that can lead to serious burns or
death. If this spray is ignited it is called “terminal
venting with ignition.”
To reduce the risk of electrocution, serious burns
or death from terminal venting with ignition:
➤
Disconnect ALL electrical power before
removing the protective terminal cover.
➤
Never energize the system unless:
•
the protective terminal cover is securely
fastened, and
•
the compressor is properly connected to
ground.
➤
Never reset a breaker or replace a fuse without
first checking for a ground fault. An open fuse
or tripped circuit breaker is a strong indication
of a ground fault.
➤
Be alert for sounds of arcing (sputtering or
popping) inside the compressor. If you hear
these sounds, IMMEDIATELY get away.
A. Checking for a Ground Fault (a Short to
Ground)
Step 1: Disconnect Power
Disconnect all electrical power supplies to the sys-
tem, making sure that all power legs are open.
(NOTE: The system may have more than one
power supply.)
Step 2: Check for a Ground Fault
Remove the protective terminal cover. If there is any
evidence of overheating at any lead, this is a good
indication that a compressor motor problem exists.
At this time, do not replace or reattach leads or con-
nectors that have been damaged by overheating.
Disconnect leads and/or remove all components
(such as relays and capacitors) from the terminal
pins.
CAUTION:
I
f a capacitor is present, using a
20,000 ohm resistor, discharge it before removing
it from the system to avoid damage to measuring
devices and risk of electric shock. W
hen removing
a current type relay, keep it upright.
Check the compressor for a ground fault using
either a megohmmeter (“megger”) or a Hi-Potential
Ground Tester (“Hi-Pot”). See Figure
4-4.
WARNING!
To reduce the risk of electrocution,
always follow the manufacturers’ procedures and
safety rules when using these devices.
Connect one lead of either the megger or Hi-Pot to
the copper suction line. Connect the other lead to
one of the terminal pins.
Repeat this procedure for the two remaining termi-
nal pins. If the instrument indicates any resistance
less than 2 megohms between any pin and the hous-
ing (copper suction line), a ground fault exists.
!
WARNING
