TEST METER OPERATION

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TEST METER OPERATION
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Electrical Test Instruments

• Analog Or Digital
• Voltmeters Measuring Potential Difference
• Ammeters Measuring Current Flow
• Clamp On
• Ohmmeters Measuring Resistance And Checking
  Continuity
• Capacitance Check Capacitors
• Multimeters VOM/DMM - All The Above

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Troubleshooting

• Need proper meters to do proper diagnostics
• Multi meter
• Amprobe

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General Awareness

• Job Site Safety
• Lock-Out/Tag-Out
• Personal Safety
• Clothing
• Lifting

• Fire
• Pressure
• Hazardous Materials
• Service Trucks
• Electrical

First Line Of Safety Trust Your Sixth Sense And
When It Tells You Not To Do Something
DONT DO IT!!!
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DIGITAL MULTI-METER
CLAMP ON AMP PROBE
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VOLT/OHM METEROPERATION
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CHECK FOR AN OPEN CIRCUIT

• A break in the continuous path of an electrical
  circuit.
• 1. Indicated by an infinity reading with an
  OHMMETER.
• 2. Indicated by a voltage reading with a VOLT
  METER.

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CHECK FOR A SHORT CIRCUIT

• When the electrons take a path back to the source
  that allows its to bypass all or most of the
  circuit resistance.
• 1. Indicated by a blown fuse read VOLTAGE
  across the fuse.
• 2. Indicated by reading INFINITE OHM across fuse.
• 3. Indicated by a ground (When electrons take a
  path back to the source that
• adds additional resistance to the circuit)
  ZERO OHMS READING at component being
  checked to ground .

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USING A VOLT METER TO CHECK FOR POWER AND POLARITY
L1 N V L1 G V N G V
L1 to N L1 to G Same /- 2 volts N to G
0
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VOLT METER

• CHECK FOR ELECTROMOTIVE FORCE EMF (POWER)

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Check for Open and closed switches
120
Load
120 vac
VOLTS
0
Load
120 vac
VOLTS
Pitting will cause a voltage drop across a set
of closed contacts.
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ELECTRICAL INDICATING DEVICES
120
0
Voltmeter

• Voltmeter

H
120 v
N
Always used in parallel with the load or the
switch to be tested.
Emergency Switch
MOTOR
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Voltage Drop

• When checking the voltage applied to a load such
  as an outdoor unit, the voltage applied should be
  measured in two steps first with the load
  de-energized and then with the load energized
• The difference between the de-energized and the
  energized voltage is referred to as the voltage
  drop

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Voltage Drop

• The voltage should not drop more than 3 of the
  de-energized applied voltage
• A voltage drop higher than 3 usually indicates
  that the gauge of the wire leading to the load is
  too small
• For example, if 223 volts were measured at the
  contactor of the outdoor unit de-energized

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Voltage Drop

• And then 220 volts were measured with the
  contactor energized
• This would indicate a voltage drop of only 1.35

This would be an acceptable voltage drop
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Voltage Drop

• However, if 223 volts were measured at the
  contactor of the outdoor unit de-energized, and
  then 210 volts were measured with the contactor
  energized
• The voltage drop would be

223 210 X 100 5.82 223
This would be an unacceptable voltage drop
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Troubleshooting Switches

• Switches that are closed will have no voltage
  drop
• Switches that are open will have line voltage
  across their terminals

Switches are wired in series with loads and are
used to control their operation, such as a low
pressure switch
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Ohm Meter

• Measures Ohms or Resistance

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8
Digital Meter OL
120 vac
Load
OHM
Digital Meter 0
0
120 vac
Load
OHM
Pitting will cause a reduced ohm reading across
a set of closed contacts.
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100
500
10


Analog scale
Never connect an Ohmmeter to an energized circuit
8
0
N
Permanent magnet
S
Coil
Iron core (bobbin)
Batteries
Zero adjustment
? Com
C S R
Compressor terminals
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Ohmmeter

• Always disconnect power to the circuit being
  tested first. Then use the Ohmmeter in parallel
  with the load or the switch to be tested.

H
Ohmmeter
120 v
N
Emergency Switch
MOTOR
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Ammeter

• Measures Amps or Current Flow

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Load
120 vac
0
AMP
Load
120 vac
6
AMP
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Ammeter
6
Ammeter
H
120 v

• Always used in series with the load or the
  circuit to be tested.

N
Emergency Switch
MOTOR
Clamp-on ammeter
Alternative method is to use a clamp-on ammeter.
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• Thank you for your time and attention