l With the ohmmeter set on its highest scale,
test for continuity between the terminals and the
shell. This procedure is shown in figure 14-33. If
continuity exists between the terminals and the
shell, there is a ground.
Test Lamp Continuity Check
The procedure for conducting a test lamp
continuity check is as follows:
l Disconnect the power and remove the wires
from the motor terminals.
l Ensure the lamp is connected in the hot
side of the line. Plug the test lamp into a
l Connect the hot-line probe to a motor
l Touch the free probe to the cleaned spot
on the shell. Ensure that a good connection is
made. If the light illuminates, there is a grounded
The megohmmeter (megger) consists of an
indicating movement for which current is supplied
by a small hand-driven generator. Figure 14-34
illustrates a typical megger used by the SEABEES.
Figure 14-34.A typical megohmmeter (megger).
Two leads are supplied, one of which is marked
Earth or Ground.
The procedure for making the megohmmeter
(high-resistance) test is as follows:
l Disconnect power and remove the wires
from the motor terminals.
l Place the megger probe marked Earth or
Ground on the motor or compressor frame.
Ensure there is a good metal-to-metal contact.
l Place the free probe on terminals C, S, and
R in sequence. If any reading of low resistance
is obtained, the motor is grounded.
You should always refer to the manufacturers
instructions when using a megger. It is also a good
idea to request assistance from a Construction
Electrical components in hermetic motor
compressor circuits that give trouble include start-
ing relays, overload protectors, and capacitors.
It is essential that a refrigeration and air-
conditioning service member be able to identify
these components and test them using the proper
equipment and procedures.
Basically there are three types of starting relays
in use. They are the current relay (magnetic type),
the voltage relay (magnetic type), and the
thermal relay (hot-wire type). In the hermetic
motor control circuit, a starting relay allows
electricity to flow through the starting winding
until the motor reaches two-thirds to three-fourths
of its rated speed. At this time, about 3 to 4
seconds after starting, it disconnects the starting
A current relay is an electromagnet, similar
to a solenoid valve, that employs a weight and
spring to hold the contacts open when the circuit
is idle. In operation the instantaneous surge of
starting current actuates the magnetic coil, caus-
ing the start winding contacts to close. This
closure allows starting current to the winding;