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HVACR214 – Electrical for Oil

Meters

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Meters

• Your meter will be your most often used tool as an HVAC technician.

• The meter should be your first tool out of the tool bag.

• The meter should be your last tool put away.• Make sure you read the manual that came with

your meter and understand all functions.

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Meter Types

• There are two basic types of meters on the market.

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Analog Meters

• Analog meters have been the work force for years.

• They where the first meters on the market.• They are extremely sensitive and do not

stand up well to being tossed around trucks.• They are still used today when technicians

are looking for extremely accurate measurements.

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Analog Meter

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Digital Meters

• Digital meters have almost completely replaced the analog ones in the industry.

• Digital meters stand up much better to being dropped, tossed around a truck and a wide range of temperatures.

• Digital meters are accurate and usually auto-range.

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Digital Meters

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Basic Electrical Rules

• There are several basic electrical rules you must understand prior to understanding what a meter is telling you.

• Most of these rules are based on voltage and resistance.

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Series

• You will sometimes hear technicians talk about things in series with something else.

• Series means “in the same line as”.• We will talk more about series circuits in the

next section.

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Series Example

The red ball is in series with the yellow and the green ball.

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Parallel

• You will also hear technicians speak about things in parallel.

• Parallel means “next to”.• We will talk more about parallel circuits in

the next section.

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Parallel Example

The red, yellow, and green balls are all in parallel with each other.

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Open Circuits

• Open Circuits are circuits that do not have a complete path for electricity to flow.

• Circuits require a source, switch, path, and load. If any of these components has a break (or open) in it the current can not complete it’s circuit.

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Open Circuit

L N

SW1B1

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Open Circuits

• When you measure voltage across an open circuit you will always get a reading of source voltage.

• When you measure resistance across an open circuit you will always get a reading of infinity (or OL).

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Closed or Complete Circuit

• A closed or complete circuit is one that has a complete path, source, switch, and load.

• The load is operational in a complete circuit.• The switch is closed in a complete circuit.

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Closed or Complete Circuit

L N

SW1B1

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Closed or Complete Circuit

• When measuring voltage across a switch in a complete circuit you will get 0 Volts.

• When measuring voltage across a complete circuit you will get source.

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Voltage across loads

• Voltage across a load is identical if the load is working or if the load is bad.

• If you have all switches closed, and measure voltage across the load the circuit is good.

• If the load is not working, then you have a bad load.

• If the load is working than the voltage you read is the voltage that load is using.

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Current (Amperage)

• The current or amperage you measure will be 0 in an open circuit.

• In a closed circuit the amperage you measure may change based on where you take your readings.

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Measurements

• Meters will measure:– Voltage– Current– Resistance– Capacitance– Frequency– Temperature

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Voltage

• Voltage will be one of the most frequent measurements you make.

• To measure voltage– 1. Turn your meter on and set it to Volts or V

depending on what your meter shows.– Make sure that your leads are plugged into the

correct place on the meter.

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Voltage

• Put the leads in parallel with (next to) the point in the circuit you are trying to measure.

• Hold the leads steady without touching any of the metal to your finders or each other.

• Watch the display until the meter stabilizes on a number. That is your reading.

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Voltage across open switch

L N

SW1B1

120 Volts

120

Voltage across an open switch is always source

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Voltage across closed switch

L N

SW1B1

120 Volts

0

Voltage across an open switch is always source

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Voltage across non-powered load

L N

SW1B1

120 Volts

0

Voltage across non-powered load is always 0

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Voltage across powered load

L N

SW1B1

120 Volts

120

Voltage across a powered load is always source

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Voltage across open load

L N

SW1B1

120 Volts

120

Voltage across an open powered load is always source

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Voltage across full circuit

L N

SW1B1

120 Volts 120

Voltage across a full circuit is always source

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Measuring Resistance

• To measure the resistance of a circuit– Disconnect the circuit from the source. With

resistance measurements there can not be any power on the circuit.

– Decide what component or portion of the circuit you would like to measure.

– Disconnect the wires to, or remove that part.

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Measuring Resistance

• Set your meter to Ohms and touch one lead directly to the other. This will show a reading of 0 on your meter.

• If it does not, check your leads for damage and make sure they are plugged into the right spots on your meter.

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Measuring Resistance

• Now touch one lead to each side of the component or isolated portion of the circuit that you are testing.

• Wait for the display to stabilize and record that number.

• This is the resistance. Resistance is shown in Ohms.

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Resistance across open switch

L N

SW1B1

120 Volts

OL

Resistance across an open switch is always OL

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Resistance across closed switch

L N

SW1B1

120 Volts

OL

Resistance across an closed switch is always 0

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Resistance across a good load

L N

SW1B1

120 Volts

#

Resistance across a good load is some number

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Resistance across an open load

L N

SW1B1

120 Volts

OL

Resistance across an open load is OL or infinity

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Measuring Current

• To measure current the first step is to determine which method you want to use.– It is possible to use the clamp for higher

voltages and currents.– It is possible to put the meter in line for lower

voltages and currents.

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Measuring Current - Clamp-on

• To measure current with the clamp-on meter– Make sure the system is running– Clamp the meter around a single wire and wait

until the numbers stabilize.– This is the amperage reading.

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Measuring Current - Clamp-on

• If the current is to low consider putting the meter in-line.

• If that is not possible wrap the wire around the clamp 5-10 times.

• Take your reading.• Divide the number you get by the number of

times the wire is wrapped around the clamp.

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Measuring Current

• For example if the wire is wrapped 10 times around the clamp and your reading is 2 amps then:– 2 / 10 = .2 amps

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Measuring Current - In Line

L N

SW1B1

120 Volts

Meter

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Measuring Current In-Line

• Make sure the power to the circuit is turned off.• Check with your voltmeter to verify this is the

case.• Disconnect a wire directly before the component

you are concerned about and put the meter in series (or in-line) with the component to complete the circuit.

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Measuring current in-line

• Make sure the meter is set to amps and the leads are plugged into the correct spots.

• Turn the circuit back on and then allow the display to stabilize on the meter.

• This is your amperage reading.

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Measuring Current In-Line

• Make sure that you know the levels of voltage and current your meter is rated for.

• Never exceed this voltage or current. If you suspect it is close use the clamp-on method.

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Hop-scotch method

• Unfortunately most of the time you will not just have one switch controlling a load.

• Most circuits in the HVAC industry will have more than one control device.

• You must have a reliable, organized method to find problems in the circuit.

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Hop-scotch method

• This is why most good technicians start off any diagnostics by using the hop-scotch method to trace circuits.

• The procedures for this is very simple.

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Hop Scotch Method

• First, make sure your meter is set on volts and make sure the leads are correctly plugged into the appropriate places on the meter.

• Next check voltage across the two endpoints of the circuit (Line and Neutral) or (line and line).

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Hop-scotch method

• Next put one lead onto the start point of the circuit, in our case L1.

• Keep that lead there.• Use the second lead to go from point to

point in the circuit (before and after each switching device and load) checking for opens until you find the problem.

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Hop Scotch Example

L N

SW1B1

120 Volts 120

Voltage across L1 and N is 120 - you have power to the circuit.

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Hop Scotch Example

L N

SW1B1

120 Volts 0

Voltage across L1 and the line side of SW1 is 0 sothe wire from L to SW1 is good.

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Hop Scotch Example

L N

SW1B1

120 Volts 120

Voltage across L1 and the load side of SW1 is 120This means that SW1 is open. Remember voltageacross and open switch is always source.

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Hop Scotch Example

L N

SW1B1

120 Volts 120

You can verify this is the problem by now startingfrom neutral.

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Hop Scotch Example

L N

SW1B1

120 Volts 0

Voltage from neutral to neutral side of B1 is 0.Wire is good.

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Hop Scotch Example

L N

SW1B1

120 Volts 0

Voltage from neutral to line side of B1 is 0.No problem, voltage remains 0.

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Hop Scotch Example

L N

SW1B1

120 Volts 120

Voltage from neutral to line side of SW1 is 120.Problem found, SW1 is open.