TEST METER OPERATION Electrical Test Instruments Analog Or

TEST METER OPERATION

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

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!!!

DIGITAL MULTI-METER CLAMP ON AMP PROBE

VOLT/OHM METER OPERATION

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 120 vac VOLTS 0 Load VOLTS Pitting will cause a voltage drop across a set of closed contacts.

ELECTRICAL INDICATING DEVICES 0 120 Voltmeter H Voltmeter 120 v N Always used in parallel with the load or the switch to be tested. Emerge ncy Switch MOTOR

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

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

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

120 vac Digital Meter: OL ∞ Load OHM 120 vac Digital Meter: 0 0 OHM Load Pitting will cause a reduced ohm reading across a set of closed contacts.

500 10 Analog scale ∞ 0 N S Never connect an Ohmmeter to an energized circuit Permanent magnet Coil Iron core (bobbin) Batteries Zero adjustment Ω Com C S R Compressor terminals

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

Ammeter Measures Amps or Current Flow

Load 120 vac 0 AMP Load 120 vac 6 AMP

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 clampon ammeter.

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