Author Topic: Electricity and Controls for HVAC/R Technicians  (Read 13421 times)

Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #15 on: December 19, 2011, 10:32:44 PM »
   Electricity is a basic part of nature and it is one of our most widely used forms of energy.
]Atoms are the building blocks of everything we know. They are so small that to see a material containing millions of them would still need a microscope.

The center of an atom is called the nucleus. It is made up of particles called protons and neutrons.
The nucleus is surrounded by minute particles called electrons that move around.
If we concentrate on just the electrons this is the part of the atom that we can call electricity.
In some materials, electrons are tightly bound to the atoms.(insulating material).  This means they don't move very much and they cannot conduct electricity very well.
In other materials like metal some electrons are very loose and move easily. (conductive material) They have electrons that can detach from their atoms and move around the structure of the material. These are called free electrons. The moving electrons transmit electrical energy from one point to another.
Electrons flow through wires, but they never leave, they just move.  For this reason you need something called a circuit.   
 
  To create an electrical force or movement a generator, alternator or battery is often used relying on magnetism or chemicals to push electrons around.  It is not so much pumping the electrons out of the wire though, as simply forcing them all to move along it. So the electrons being pushed out one side of a piece of wire and a new electron follows behind it.
In magnetism, most of the electrons at one end are spinning in one direction.  At the other end electrons are spinning in the opposite direction. 
This is unlike other materials as usually electrons are in balance spinning 50% either way along the whole structure. 
For this reason magnets can be used to make electricity. Moving magnetic fields can pull and push electrons and start moving electrons in a circuit.

A water analogy is often used to help describe how an electrical circuit works.  Consider a water pump driving water through a closed loop of piping.  The pump never runs out of water (any more than an electrical circuit runs out of electrons) since the water circulated by the pump pushing against the water already in the pipe until it arrives back to the pump.
So now we have this energy moving around wires we can begin to control it and use it for our own advantage



 
« Last Edit: December 19, 2011, 10:38:03 PM by Icehouse »
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #16 on: December 19, 2011, 10:40:36 PM »
Electricity is made in Power Stationsby huge generators powered by coal, nucleur, natural gas, water or even wind.
The basic principle of a generator has two main components: a rotating magnet called the “rotor” which turns inside stationary coils of copper wire called the “stator.”

When the rotor rotates through the magnetic field, it generates a flow of current through the copper coils of the stator. Generating plants must use some form of energy or fuel to turn the rotor mentioned above.

Electricity is produced, sent through very high voltage transmission lines to substations.
At substations, the voltage of the electric power is lowered. Voltage is the force that pushes electricity along wires. Then, the power is sent to your neighborhood through distribution lines located underground or on poles.
After electricity is produced at power plants it has to get to the customers that need the electricity.
The electricity first goes to a transformer at the power plant that boosts the voltage up to 100,000's of volts. When electricity travels long distances it is better to have it at higher voltages as it can be transferred more efficiently this way.
The long thick cables of transmission lines are made of copper or aluminum because they have a low resistance. Some of the electrical energy is lost because it is changed into heat energy. High voltage transmission lines carry electricity long distances to a substation.
The power lines go into substations near businesses, factories and homes. Here transformers change the very high voltage electricity back into lower voltage electricity.
From these substations , electricity in different power levels is used to run factories, streetcars and mass transit, light street lights and stop lights, and is sent to your neighborhood.
Electricity enters your home or premises through a meter.
It then goes to the circuit panel or control panel which then distributes the different circuits that power you house.
Traditionally, the UK has had a 240 electrical supply since the 1960s. Continental Europe had a 220V, and Ireland a 230V, supply.  The USA and Canada are supplied by 120 volts mains connection.
NATE, NCCER, PHCC,HVAC Certified Instructor
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #17 on: December 19, 2011, 10:42:08 PM »
 Electrons need something to make them move from atom to atom through a circuit. When electrons are flowing, there has to an electrical force somewhere pushing the electrons. Without a push everything would stay relatively static and we would have no flow of energy.
This is what is know as voltage.
Voltage is measured in volts.
The supply of voltage to domestic and small commercial premises varies in different countries and it is essential to know this.
In general you can split it up into two parts of the world:
120 and 220 Volt; (USA)
230 Volt (Europe & Asia)
NATE, NCCER, PHCC,HVAC Certified Instructor
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #18 on: December 19, 2011, 10:43:34 PM »
If volts are the force pushing electrons throught metal, amperes or amps for short is the amount of current flowing in a circuit. The more current flowing, the higher the amps.
This flow of electrical current develops when electrons are forced from one atom to another.  Current is a measure of the rate of electron flow through a material. Electrical current is measured in units of amperes or "amps" for short.
Thinking of electricity as like water, and a wire as like a hose is a popular analogy. How would you measure the water coming out of the hose?
There are two ways:
The pressure pushing the water (voltage)
The amount of water that flows through the hose every second (Amps)

The latter would be the most comparable to the measure of amps running through a cable. 
A multimeter can be used to test how many amps are flowing through a wire at a given time.
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #19 on: December 19, 2011, 10:44:56 PM »
 Watts are a measure of the rate at which electricity does its work or provides energy.
e.g, the power used to run an electric fire could be 2000 watts.
Watts (W) are the units in which electric power is commonly measured. 
Wattage is calculated by using the following equation: Watts = Volts x Amps
The electricity in your home is 120 volts depending where you are in the world.
A light bulb for example operates at 1 amp.
If we use the above equation
120(volts) x 0.5 (amps)  = 60 Watts
 
According to the equation for power, multiplying these two numbers gives the bulb's wattage, which in this case is 60 watts.
The wattage tells you the power of the bulb, or the rate at which energy is being delivered.
The higher the wattage of bulb, the brighter the bulb and the more power it uses, also the more expensive it is to run.
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #20 on: December 19, 2011, 10:46:52 PM »
Resistance is a force which opposes the flow of an electric current around a circuit.  Voltage is required to push the charged particles around the circuit to push through resistance. The circuit itself will resist the flow of particles especially if the wires are either very thin or very long. There are three main factors that effect resistance in an electrical circuit.
 
1 - The type of material - Electrons find it easier to pass through some materials than others such as metal. 
2 - The length of the wire in a circuit - If the length of a wire is doubled, the resistance is also doubled. This is because twice the length of wire is equivalent to two equal resistances in series. 3 - Thickness of a wire - A thicker wire has a  larger cross section and more electrons. This enables more electric current pass through on a given voltage with less resistance.. When electrons move against the opposition of resistance, "friction" is generated. Just like mechanical friction, the friction produced by electrons flowing against a resistance generates heat energy. A good example of friction at work is a lamp's filament. The lamp has a very thin wire and the friction being created by electric current passing through it causes a large amount of heat energy being manifested at that filament. This heat energy is enough to cause the filament to glow white-hot, producing light, whereas the wires connecting the lamp to the battery (which have much lower resistance) hardly even get warm while conducting the same amount of current. A resistor is a component of an electrical circuit that is specially resists the flow of electrical current. A resistor has two terminals across which electricity must pass, and is designed to drop the voltage of the current as it flows from one terminal to the next. A resistor is primarily used to create and maintain a known safe current within an electrical component.
Resistance and the Ohm
Resistance is measured in Ohms  (symbol: Ω) .
The bigger the resistance, the smaller the current.
An ohm (symbol: Ω) is a resistance in a conductor that produces a potential difference of one volt when a current of one amp is flowing through it.
To calculate the resistance of a component. Firstly, we need to measure the current flowing through it, and the voltage across the component.
If the ammeter reads 3 A, and the voltmeter reads 9 V across the component,.
Resistance = Volts divided by current (amps).
    R = V / I
   
R = 9 / 3
    R = 3 Ohms
« Last Edit: December 19, 2011, 10:51:00 PM by Icehouse »
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #21 on: December 20, 2011, 08:38:56 AM »
  Ammeter usage


PARTS AND MATERIALS
  • 6-volt battery
  • 6-volt incandescent lamp


 LEARNING OBJECTIVES
 
  • How to measure current with a multimeter
  • How to check a multimeter's internal fuse
  • Selection of proper meter range
SCHEMATIC DIAGRAM


 ILLUSTRATION


 INSTRUCTIONS Current is the measure of the rate of electron "flow" in a circuit. It is measured in the unit of the Ampere, simply called "Amp," (A).
The most common way to measure current in a circuit is to break the circuit open and insert an "ammeter" in series (in-line) with the circuit so that all electrons flowing through the circuit also have to go through the meter. Because measuring current in this manner requires the meter be made part of the circuit, it is a more difficult type of measurement to make than either voltage or resistance.
Some digital meters, like the unit shown in the illustration, have a separate jack to insert the red test lead plug when measuring current. Other meters, like most inexpensive analog meters, use the same jacks for measuring voltage, resistance, and current. Consult your owner's manual on the particular model of meter you own for details on measuring current.
When an ammeter is placed in series with a circuit, it ideally drops no voltage as current goes through it. In other words, it acts very much like a piece of wire, with very little resistance from one test probe to the other. Consequently, an ammeter will act as a short circuit if placed in parallel (across the terminals of) a substantial source of voltage. If this is done, a surge in current will result, potentially damaging the meter:
  Ammeters are generally protected from excessive current by means of a small fuse located inside the meter housing. If the ammeter is accidently connected across a substantial voltage source, the resultant surge in current will "blow" the fuse and render the meter incapable of measuring current until the fuse is replaced. Be very careful to avoid this scenario!
You may test the condition of a multimeter's fuse by switching it to the resistance mode and measuring continuity through the test leads (and through the fuse). On a meter where the same test lead jacks are used for both resistance and current measurement, simply leave the test lead plugs where they are and touch the two probes together. On a meter where different jacks are used, this is how you insert the test lead plugs to check the fuse:

Build the one-battery, one-lamp circuit using jumper wires to connect the battery to the lamp, and verify that the lamp lights up before connecting the meter in series with it. Then, break the circuit open at any point and connect the meter's test probes to the two points of the break to measure current. As usual, if your meter is manually-ranged, begin by selecting the highest range for current, then move the selector switch to lower range positions until the strongest indication is obtained on the meter display without over-ranging it. If the meter indication is "backwards," (left motion on analog needle, or negative reading on a digital display), then reverse the test probe connections and try again. When the ammeter indicates a normal reading (not "backwards"), electrons are entering the black test lead and exiting the red. This is how you determine direction of current using a meter. For a 6-volt battery and a small lamp, the circuit current will be in the range of thousandths of an amp, or milliamps. Digital meters often show a small letter "m" in the right-hand side of the display to indicate this metric prefix.
Try breaking the circuit at some other point and inserting the meter there instead. What do you notice about the amount of current measured? Why do you think this is?
Re-construct the circuit on a breadboard like this:

Students often get confused when connecting an ammeter to a breadboard circuit. How can the meter be connected so as to intercept all the circuit's current and not create a short circuit? One easy method that guarantees success is this:
 
  • Identify what wire or component terminal you wish to measure current through.
  • Pull that wire or terminal out of the breadboard hole. Leave it hanging in mid-air.
  • Insert a spare piece of wire into the hole you just pulled the other wire or terminal out of. Leave the other end of this wire hanging in mid-air.
  • Connect the ammeter between the two unconnected wire ends (the two that were hanging in mid-air). You are now assured of measuring current through the wire or terminal initially identified.

Again, measure current through different wires in this circuit, following the same connection procedure outlined above. What do you notice about these current measurements? The results in the breadboard circuit should be the same as the results in the free-form (no breadboard) circuit.
Building the same circuit on a terminal strip should also yield similar results:

The current figure of 24.70 milliamps (24.70 mA) shown in the illustrations is an arbitrary quantity, reasonable for a small incandescent lamp. If the current for your circuit is a different value, that is okay, so long as the lamp is functioning when the meter is connected. If the lamp refuses to light when the meter is connected to the circuit, and the meter registers a much greater reading, you probably have a short-circuit condition through the meter. If your lamp refuses to light when the meter is connected in the circuit, and the meter registers zero current, you've probably blown the fuse inside the meter. Check the condition of your meter's fuse as described previously in this section and replace the fuse if necessary.
   
« Last Edit: December 20, 2011, 08:40:55 AM by Icehouse »
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #22 on: December 20, 2011, 08:45:35 AM »
   Ohmmeter usage PARTS AND MATERIALS 
  • Multimeter, digital or analog
  • Assorted resistors (Radio Shack catalog # 271-312 is a 500-piece assortment)
  • Rectifying diode (1N4001 or equivalent; Radio Shack catalog # 276-1101)
  • Cadmium Sulphide photocell (Radio Shack catalog # 276-1657)
  • Breadboard (Radio Shack catalog # 276-174 or equivalent)
  • Jumper wires
  • Paper
  • Pencil
  • Glass of water
  • Table salt
This experiment describes how to measure the electrical resistance of several objects. You need not possess all items listed above in order to effectively learn about resistance. Conversely, you need not limit your experiments to these items. However, be sure to never measure the resistance of any electrically "live" object or circuit. In other words, do not attempt to measure the resistance of a battery or any other source of substantial voltage using a multimeter set to the resistance ("ohms") function. Failing to heed this warning will likely result in meter damage and even personal injury.
 



 LEARNING OBJECTIVES
 
  • Determination and comprehension of "electrical continuity"
  • Determination and comprehension of "electrically common points"
  • How to measure resistance
  • Characteristics of resistance: existing between two points
  • Selection of proper meter range
  • Relative conductivity of various components and materials


 ILLUSTRATION

 

 INSTRUCTIONS Resistance is the measure of electrical "friction" as electrons move through a conductor. It is measured in the unit of the "Ohm," that unit symbolized by the capital Greek letter omega (Ω).
Set your multimeter to the highest resistance range available. The resistance function is usually denoted by the unit symbol for resistance: the Greek letter omega (Ω), or sometimes by the word "ohms." Touch the two test probes of your meter together. When you do, the meter should register 0 ohms of resistance. If you are using an analog meter, you will notice the needle deflect full-scale when the probes are touched together, and return to its resting position when the probes are pulled apart. The resistance scale on an analog multimeter is reverse-printed from the other scales: zero resistance in indicated at the far right-hand side of the scale, and infinite resistance is indicated at the far left-hand side. There should also be a small adjustment knob or "wheel" on the analog multimeter to calibrate it for "zero" ohms of resistance. Touch the test probes together and move this adjustment until the needle exactly points to zero at the right-hand end of the scale. Although your multimeter is capable of providing quantitative values of measured resistance, it is also useful for qualitative tests of continuity: whether or not there is a continuous electrical connection from one point to another. You can, for instance, test the continuity of a piece of wire by connecting the meter probes to opposite ends of the wire and checking to see the the needle moves full-scale. What would we say about a piece of wire if the ohmmeter needle didn't move at all when the probes were connected to opposite ends?
Digital multimeters set to the "resistance" mode indicate non-continuity by displaying some non-numerical indication on the display. Some models say "OL" (Open-Loop), while others display dashed lines. Use your meter to determine continuity between the holes on a breadboard: a device used for temporary construction of circuits, where component terminals are inserted into holes on a plastic grid, metal spring clips underneath each hole connecting certain holes to others. Use small pieces of 22-gauge solid copper wire, inserted into the holes of the breadboard, to connect the meter to these spring clips so that you can test for continuity:

 

   An important concept in electricity, closely related to electrical continuity, is that of points being electrically common to each other. Electrically common points are points of contact on a device or in a circuit that have negligible (extremely small) resistance between them. We could say, then, that points within a breadboard column (vertical in the illustrations) are electrically common to each other, because there is electrical continuity between them. Conversely, breadboard points within a row (horizontal in the illustrations) are not electrically common, because there is no continuity between them. Continuity describes what is between points of contact, while commonality describes how the points themselves relate to each other.
Like continuity, commonality is a qualitative assessment, based on a relative comparison of resistance between other points in a circuit. It is an important concept to grasp, because there are certain facts regarding voltage in relation to electrically common points that are valuable in circuit analysis and troubleshooting, the first one being that there will never be substantial voltage dropped between points that are electrically common to each other. Select a 10,000 ohm (10 kΩ) resistor from your parts assortment. This resistance value is indicated by a series of color bands: Brown, Black, Orange, and then another color representing the precision of the resistor, Gold (+/- 5%) or Silver (+/- 10%). Some resistors have no color for precision, which marks them as +/- 20%. Other resistors use five color bands to denote their value and precision, in which case the colors for a 10 kΩ resistor will be Brown, Black, Black, Red, and a fifth color for precision.
Connect the meter's test probes across the resistor as such, and note its indication on the resistance scale:

If the needle points very close to zero, you need to select a lower resistance range on the meter, just as you needed to select an appropriate voltage range when reading the voltage of a battery. If you are using a digital multimeter, you should see a numerical figure close to 10 shown on the display, with a small "k" symbol on the right-hand side denoting the metric prefix for "kilo" (thousand). Some digital meters are manually-ranged, and require appropriate range selection just as the analog meter. If yours is like this, experiment with different range switch positions and see which one gives you the best indication.
Try reversing the test probe connections on the resistor. Does this change the meter's indication at all? What does this tell us about the resistance of a resistor? What happens when you only touch one probe to the resistor? What does this tell us about the nature of resistance, and how it is measured? How does this compare with voltage measurement, and what happened when we tried to measure battery voltage by touching only one probe to the battery?
When you touch the meter probes to the resistor terminals, try not to touch both probe tips to your fingers. If you do, you will be measuring the parallel combination of the resistor and your own body, which will tend to make the meter indication lower than it should be! When measuring a 10 kΩ resistor, this error will be minimal, but it may be more severe when measuring other values of resistor.
You may safely measure the resistance of your own body by holding one probe tip with the fingers of one hand, and the other probe tip with the fingers of the other hand. Note: be very careful with the probes, as they are often sharpened to a needle-point. Hold the probe tips along their length, not at the very points! You may need to adjust the meter range again after measuring the 10 kΩ resistor, as your body resistance tends to be greater than 10,000 ohms hand-to-hand. Try wetting your fingers with water and re-measuring resistance with the meter. What impact does this have on the indication? Try wetting your fingers with saltwater prepared using the glass of water and table salt, and re-measuring resistance. What impact does this have on your body's resistance as measured by the meter? Resistance is the measure of friction to electron flow through an object. The less resistance there is between two points, the harder it is for electrons to move (flow) between those two points. Given that electric shock is caused by a large flow of electrons through a person's body, and increased body resistance acts as a safeguard by making it more difficult for electrons to flow through us, what can we ascertain about electrical safety from the resistance readings obtained with wet fingers? Does water increase or decrease shock hazard to people? Measure the resistance of a rectifying diode with an analog meter. Try reversing the test probe connections to the diode and re-measure resistance. What strikes you as being remarkable about the diode, especially in contrast to the resistor?
Take a piece of paper and draw a very heavy black mark on it with a pencil (not a pen!). Measure resistance on the black strip with your meter, placing the probe tips at each end of the mark like this:

Move the probe tips closer together on the black mark and note the change in resistance value. Does it increase or decrease with decreased probe spacing? If the results are inconsistent, you need to redraw the mark with more and heavier pencil strokes, so that it is consistent in its density. What does this teach you about resistance versus length of a conductive material? Connect your meter to the terminals of a cadmium-sulphide (CdS) photocell and measure the change in resistance created by differences in light exposure. Just as with the light-emitting diode (LED) of the voltmeter experiment, you may want to use alligator-clip jumper wires to make connection with the component, leaving your hands free to hold the photocell to a light source and/or change meter ranges:

Experiment with measuring the resistance of several different types of materials, just be sure not to try measure anything that produces substantial voltage, like a battery. Suggestions for materials to measure are: fabric, plastic, wood, metal, clean water, dirty water, salt water, glass, diamond (on a diamond ring or other piece of jewelry), paper, rubber, and oil.
   
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Offline Icehouse

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #23 on: December 20, 2011, 08:51:37 AM »
     Voltmeter usage     PARTS AND MATERIALS
  • Multimeter, digital or analog
  • Assorted batteries
  • One light-emitting diode (Radio Shack catalog # 276-026 or equivalent)
  • Small "hobby" motor, permanent-magnet type (Radio Shack catalog # 273-223 or equivalent)
  • Two jumper wires with "alligator clip" ends (Radio Shack catalog # 278-1156, 278-1157, or equivalent)
A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointer over a printed scale.
Analog multimeters tend to be less expensive than digital multimeters, and more beneficial as learning tools for the first-time student of electricity. I strongly recommend purchasing an analog multimeter before purchasing a digital multimeter, but to eventually have both in your tool kit for these experiments.

 CROSS-REFERENCES
Lessons In Electric Circuits, Volume 1, chapter 1: "Basic Concepts of Electricity"
Lessons In Electric Circuits, Volume 1, chapter 8: "DC Metering Circuits"

 LEARNING OBJECTIVES
 
  • How to measure voltage
  • Characteristics of voltage: existing between two points
  • Selection of proper meter range

 ILLUSTRATION

 

 

 INSTRUCTIONS
In all the experiments in this book, you will be using some sort of test equipment to measure aspects of electricity you cannot directly see, feel, hear, taste, or smell. Electricity -- at least in small, safe quantities -- is insensible by our human bodies. Your most fundamental "eyes" in the world of electricity and electronics will be a device called a multimeter. Multimeters indicate the presence of, and measure the quantity of, electrical properties such as voltage, current, and resistance. In this experiment, you will familiarize yourself with the measurement of voltage. Voltage is the measure of electrical "push" ready to motivate electrons to move through a conductor. In scientific terms, it is the specific energy per unit charge, mathematically defined as joules per coulomb. It is analogous to pressure in a fluid system: the force that moves fluid through a pipe, and is measured in the unit of the Volt (V).
Your multimeter should come with some basic instructions. Read them well! If your multimeter is digital, it will require a small battery to operate. If it is analog, it does not need a battery to measure voltage. Some digital multimeters are autoranging. An autoranging meter has only a few selector switch (dial) positions. Manual-ranging meters have several different selector positions for each basic quantity: several for voltage, several for current, and several for resistance. Autoranging is usually found on only the more expensive digital meters, and is to manual ranging as an automatic transmission is to a manual transmission in a car. An autoranging meter "shifts gears" automatically to find the best measurement range to display the particular quantity being measured.
Set your multimeter's selector switch to the highest-value "DC volt" position available. Autoranging multimeters may only have a single position for DC voltage, in which case you need to set the switch to that one position. Touch the red test probe to the positive (+) side of a battery, and the black test probe to the negative (-) side of the same battery. The meter should now provide you with some sort of indication. Reverse the test probe connections to the battery if the meter's indication is negative (on an analog meter, a negative value is indicated by the pointer deflecting left instead of right). If your meter is a manual-range type, and the selector switch has been set to a high-range position, the indication will be small. Move the selector switch to the next lower DC voltage range setting and reconnect to the battery. The indication should be stronger now, as indicated by a greater deflection of the analog meter pointer (needle), or more active digits on the digital meter display. For the best results, move the selector switch to the lowest-range setting that does not "over-range" the meter. An over-ranged analog meter is said to be "pegged," as the needle will be forced all the way to the right-hand side of the scale, past the full-range scale value. An over-ranged digital meter sometimes displays the letters "OL", or a series of dashed lines. This indication is manufacturer-specific.
What happens if you only touch one meter test probe to one end of a battery? How does the meter have to connect to the battery in order to provide an indication? What does this tell us about voltmeter use and the nature of voltage? Is there such a thing as voltage "at" a single point?
Be sure to measure more than one size of battery, and learn how to select the best voltage range on the multimeter to give you maximum indication without over-ranging. Now switch your multimeter to the lowest DC voltage range available, and touch the meter's test probes to the terminals (wire leads) of the light-emitting diode (LED). An LED is designed to produce light when powered by a small amount of electricity, but LEDs also happen to generate DC voltage when exposed to light, somewhat like a solar cell. Point the LED toward a bright source of light with your multimeter connected to it, and note the meter's indication:
  Batteries develop electrical voltage through chemical reactions. When a battery "dies," it has exhausted its original store of chemical "fuel." The LED, however, does not rely on an internal "fuel" to generate voltage; rather, it converts optical energy into electrical energy. So long as there is light to illuminate the LED, it will produce voltage. Another source of voltage through energy conversion a generator. The small electric motor specified in the "Parts and Materials" list functions as an electrical generator if its shaft is turned by a mechanical force. Connect your voltmeter (your multimeter, set to the "volt" function) to the motor's terminals just as you connected it to the LED's terminals, and spin the shaft with your fingers. The meter should indicate voltage by means of needle deflection (analog) or numerical readout (digital). If you find it difficult to maintain both meter test probes in connection with the motor's terminals while simultaneously spinning the shaft with your fingers, you may use alligator clip "jumper" wires like this:
  Determine the relationship between voltage and generator shaft speed? Reverse the generator's direction of rotation and note the change in meter indication. When you reverse shaft rotation, you change the polarity of the voltage created by the generator. The voltmeter indicates polarity by direction of needle direction (analog) or sign of numerical indication (digital). When the red test lead is positive (+) and the black test lead negative (-), the meter will register voltage in the normal direction. If the applied voltage is of the reverse polarity (negative on red and positive on black), the meter will indicate "backwards."
   
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline Icehouse

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    • hvacbob
Re: Electricity and Controls for HVAC/R Technicians
« Reply #24 on: December 20, 2011, 08:56:54 AM »
 Refrigerator starting relay, starting Capacitor and overload Protector.
   Starting Relay
The compressor motor employs both a start and run winding. The run winding is energized during the complete cycle of operation, whereas the start winding is energized only during the starting period. The current-operated type of relay has a coil connected in series with the run winding of the compressor. Some current-operated relays plug directly onto the compressor while others do not. Most relays are mounted in a case located on the compressor. When the thermostat closes, the compressor attempts to start, drawing heavy current through the run winding and the relay coil. This strong current flow through the relay coil creates a magnetic field strong enough to cause the start contacts to lift and close, energizing the start winding. When the compressor reaches approximately 3/4 running speed, the current flow through the relay coil decreases (due to the countering electrical magnetic field in the motor) and as the magnet weakens, the start contacts fall open. This type of relay must be used with an overload protector and must be mounted in an upright position, so that the contacts can fall freely to the "open" position.

   Overload Protector
The bimetallic overload protector is mounted in series with the motor windings. Should the current in the motor windings increase to a dangerous value, the heat developed by the passage of the current through the protector will cause it to open. This breaks the circuit to the motor windings and stops the motor before any damage can occur.

                                                                                    Starting Capacitor
  The starting capacitor (when required) is momentarily placed in series with the start winding to increase the starting torque of the compressor. The starting capacitor drops out of the circuit as soon as the start contacts fall to the "open" position.


                                                 Testing the Capacitor

Before testing the capacitor, disconnect the power supply and place the capacitor in a Capacitor Analyzer. If an analyzer is not available, follow the procedure below.

[/b]
  Ohmmeter Test
  Before testing the capacitor, disconnect the power supply and remove all wiring to the capacitor. Discharge the capacitor using a 20,000-ohm, 2-watt resistor, by placing the resistor across the capacitor terminals. Set the ohmmeter on the highest resistance scale and attach the leads to the capacitor terminals. The needle should deflect instantly toward zero and return slowly to infinity. This should occur each time the leads are reversed. This indicates the capacitor is not shorted or open. If the needle stays at or near zero or remains on infinity, the capacitor is defective and should be replaced. Be sure to reverse leads and check again before condemning the capacitor.
« Last Edit: December 20, 2011, 09:06:03 AM by Icehouse »
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline Icehouse

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    • hvacbob
Re: Electricity and Controls for HVAC/R Technicians
« Reply #25 on: December 20, 2011, 09:11:46 AM »
         

 
   
Thermostat Terminal Designation Color of Wire and Termination
R – The R terminal is the power for the thermostat. This comes from the transformer usually located in the blower section for split systems but you may find the transformer in the condensing unit. For this reason, it is a good idea to kill the power at the condenser  and the air handler before changing or working on the wiring at the thermostat. If you have a package unit then the transformer is in the package unit. Red for the R terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding.
RC – The RC terminal is designated for the power for cooling. Some HVAC systems use two transformers. A transformer for cooling and a transformer for heating. In this case the power from the transformer in the air conditioning system would go to the thermostat terminal. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer. Red for RC terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.
RH – The RH terminal is designated for the power for heating. See RC above for an explanation. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer. Red for RH terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.
Y – This is the terminal for cooling or air conditioning and goes to the compressor relay. Typically a thermostat wire pull is made to the air handler on split systems and then this wire is spliced for the separate wire pull which is made to the condenser. Some manufacturers put a terminal board strip near the control board in the air handler so a splice is not needed. Yellow for Y Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.
Y2 – This is the thermostat terminal for cooling second stage if your system is so equipped. Many systems only have a single compressor but if you have two compressors which should only operate off of one thermostat then you need the Y2 thermostat terminal for second stage cooling. *The most common color I’ve seen used for this terminal and wire designation is light blue but this varies and is completely up to the installer what color to use. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.
W – This is the thermostat terminal for heating. This wire should go directly to the heating source whether it be a gas or oil furnace, electric furnace, or boiler, White for W Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.
W2 – This is the thermostat terminal used for second stage heat. There are gas furnaces with low fire and high fire and some depend on control from a two-stage heating thermostat with a W2 terminal. Heat Pumps  use staging for auxiliary heat and need a W2 terminal. *The most common color I’ve seen used for this terminal and wire designation is brown but this varies and is completely up to the installer what color to use.
G – This is the thermostat terminal used for the fan relay to energize the indoor blower fan. On a split system the blower fan is in the air handler while with a package unit the blower fan is in the outdoor package unit. Green for G Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.
C – This is the thermostat terminal which originates from the transformer and is necessary to complete the 24 volts power circuit in the thermostat but only if the thermostat consumes electricity for power. Many digital thermostats require 24 volts for power so the common wire is necessary. C stands for common and there is no universal color used for this terminal although black is the most common color I’ve seen.
O or B – These thermostat terminals are for heat pumps and the B thermostat terminal is used on for Rheem or Ruud and any manufacturer that energizes the reversing valve in heating mode for the heat pump. Most other manufacturers of heat pumps will utilize the reversing valve for cooling and the O thermostat terminal will be utilized for this purpose. This wire goes to outside heat pump condenser where the reversing valve is located. Orange for O and Dark Blue for B depending on the installer of the heat pump and the manufacturer. If you have a Trane, Carrier, Goodman, Lennox, Ducane, Heil, Fedders, Amana, Janitrol, or any other manufacturer other than Rheem or Ruud you will be utilizing the orange wire for reversing valve. Rheem and Ruud will usually utilize the blue wire for reversing valve.
E – This thermostat terminal is for heat pumps and stands for Emergency Heating. If for whatever reason the heat pump condenser fails and it is necessary to run the heat there is an option on heat pump thermostats for emergency heating. Basically this simply utilizes the back-up heat source many heat pumps have to heat the home without sending a signal to the condenser to run for heat. E – There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the E terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.
X or Aux – This thermostat terminal is for back-up on a heat pump and allows for auxiliary heating from the back-up heat source usually located in the air handler. X or Aux - There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the Aux terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.
S1 & S2 or Outdoor 1 and Outdoor 2 – Some thermostats have this terminal and it used for an outdoor temperature sensor. The wire uses for this should be special shielded wire and completely separate form the other thermostat wires. Using shielded wire prevents electromagnetic forces generated from other wires from interfering with the signal inside the shielded wire. A remote temperature sensor is a solid state device and the signal needed to get an accurate temperature is sensitive to electromagnetic forces from other wiring inside the structure.
[/t][/t]

 

 
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline niobrara

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Re: Electricity and Controls for HVAC/R Technicians
« Reply #26 on: December 20, 2011, 06:47:39 PM »
Keep it coming , it has been a few years but I am loving the reviews. Icehouse you are a great instructor. Man the stuff I have forgotten.

Offline Icehouse

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    • hvacbob
Re: Electricity and Controls for HVAC/R Technicians
« Reply #27 on: December 21, 2011, 02:40:52 PM »
Keep it coming , it has been a few years but I am loving the reviews. Icehouse you are a great instructor. Man the stuff I have forgotten.
Aw shucks I try :)
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline Icehouse

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    • hvacbob
Re: Electricity and Controls for HVAC/R Technicians
« Reply #28 on: December 22, 2011, 03:55:33 PM »
To prevent contactors from burning out
 
 Connect a 2 watt 20,00 ohm resistor on each side of the contactor, so when the points open, it takes care of the arcing that may occur.
In other words if you have a black wire to the contactor, connect it to the black wire side L1, then to the other black wire side of the contactor to the compressor.
The bleed resistor is the same ones used on start caps and run caps for the same reason.
   
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline Icehouse

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    • hvacbob
Re: Electricity and Controls for HVAC/R Technicians
« Reply #29 on: December 22, 2011, 03:57:55 PM »
On most single-phase compressors with a single-pole contactor, there is a solid bar on one side of the contactor instead of having two contacts. One leg of power passes down the bar to the capacitor and to the run winding. It passes through the run winding of the compressor and from common back to the contactor. It lands on the load side of the normally open contact of the contactor. At off cycle, line voltage will be read from one side of the normally open contact to the other: Line 1 on the line side and Line 2 on the load side via the windings. This acts as a cranlcase heater.
On units with an add on crankcase heater,the crankcase heater will be attached to the contactor with one leg on the load side and one on the line side of the normally open contacts. At off cycle it will have line voltage applied to it and will heat the crankcase. Once the contactor is energized, both the line and load side of the normally open contacts become one. Since you cannot feed a load with one line of power, the crankcase heater will not work again until the contactor opens. This is a simple way to turn the crankcase heater off during the on cycle and to turn it on at the off cycle. Exercise caution when checking this type of setup because power is always present on the load side of the contactor.
« Last Edit: December 22, 2011, 04:00:25 PM by Icehouse »
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

 

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