TEST METER OPERATION

Electrical Test InstrumentsAnalog 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

Troubleshooting

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

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

DON’T DO IT!!!

24.0

L1 N

R Fan onFan Relay

Compressor Contactor coilY

G

C

DIGITAL MULTI-METER

CLAMP ONAMP PROBE

VOLT/OHM METEROPERATION

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.

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 .

VOLT METER

CHECK FOR ELECTROMOTIVE FORCE – EMF (POWER)

Check for Open and closed switches

Load120

VOLTS

0

VOLTS

Load120 vac

120 vac

Pitting will cause a voltage drop across a set of closed contacts.

ELECTRICAL INDICATING DEVICES

VoltmeterAlways used in parallel with the load or the

switch to be tested.

N

H120 v

MOTOR

Voltmeter

Emergency Switch

0 120

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

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…

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

%35.1100 x223

220223

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:

This would be an unacceptable voltage drop

223 – 210 X 100 = 5.82% 223

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

Ohm Meter

Measures Ohms or Resistance

Load OHM

Load

0

OHM

Digital Meter: OL

Digital Meter: 0

120 vac

120 vac

Pitting will cause a reduced ohm reading across a set of closed contacts.

∞

N S

∞ 0

BatteriesZero adjustment

C

S R

Ω Com

Analog scale

Permanent magnet

Iron core (bobbin)

Coil

Compressor terminals

100 500 10

Never connect an Ohmmeter to an energized circuit

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.

Ohmmeter120 v

N

H

MOTOR

EmergencySwitch

Ammeter

Measures Amps or Current Flow

Load

AMP

0

120 vac

Load

AMP

6

120 vac

Ammeter

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

Ammeter

MOTOR

120 v

N

H

Clamp-on ammeter

Alternative method is to use a clamp-on ammeter.

EmergencySwitch

6

Thank you for your time and attention