356 Section 3 Fundamentals of Electricity and Electronics
WARNING
A capacitor can store an electric
charge. You should always ground
the capacitor lead before testing
the capacitor. A capacitor cannot hurt you, but
it can startle you enough to make you jump and
be injured. You also do not want a capacitor to
discharge into and damage your ohmmeter.
To test a capacitor, you can use either an ohmmeter
or a capacitor tester. To use a capacitor tester, follow
the manufacturer’s directions. To use an ohmmeter,
disconnect and ground the capacitor’s lead. Connect
the ohmmeter leads across the capacitor as shown in
Figure 22-37. At fi rst, the ohmmeter should show low
resistance as the capacitor takes a charge from the ohm-
meter batteries. As the capacitor approaches its full
charge, the ohmmeter reading should increase to infi -
nite resistance. This shows that it is blocking dc current
but storing voltage.
Figure 22-33. A variable resistor, or potentiometer, should have
a specifi c resistance reading at each position. Compare your
readings with those given in the service manual. (Union Electronics)
Figure 22-34. A bad switch may be shorted closed or burned
open. Resistance should be zero when the switch is closed
and infi nite when the switch is open.
Figure 22-35. A transducer switch may be open or shorted
closed, or its resistance may be higher than normal. It is
normally easy to remove the wires and measure the transducer’s
resistance. You can also use a jumper wire to bypass the
transducer switch to see if the circuit begins to function.
Variable Resistor at a Low-Resistance Position
Variable Resistor at a High-Resistance Position
~V
OFF
V
Ω
mA
mA
A
~
∞
Ohmmeter reading changes
from zero to infinite
Move switch
on and off
Ohmmeter leads
Transducer switch
Make sure
resistance is
within specs
for specific
condition
Bypass switch to see if circuit begins to function
~V
OFF
V
Ω
mA
mA
A
~