I want to cover in a practical way the failures and troubles that occur in the air conditioning field. If you analyze air conditioning failures, you find that 80 percent of them are electrical failures. The remaining 20 percent of the problems are in the closed refrigerant system. With this in mind, the book is focused on 80 percent electrical malfunctions and 20 percent on closed system failure. If you look at the books on library shelves concerning air conditioning and refrigeration, much of the texts are not relevant to the field. They might have one or two chapters on electrical failures. I have written this book so the student or professional will be able to go into the field with a few tools and diagnose problems.
With this in mind, I begin with basic electricity. High-voltage transmission wires are carried within insulators on top of cross-members of power poles. Voltages are quite high; they can be 4160 volts, 3600 volts, 2400 volts, or higher. The purpose of using high voltage is to reduce wire resistance line losses.
Figure 1-1 shows distribution from network to step-down transformer with the primary attached to the high-voltage top cross bar conductors. The secondary of this transformer has a center-tap neutral and two line wires. Line one and line two are connected to the lower conductors on the bottom cross bars of the power poles. In the schematic, the secondary wires are leaving the transformer and are wired to an electrical watt-hour meter that records energy consumed.
Fig. 1-1. Electricity distribution from the network to the step-down transformer.
From the bottom of the meter, the conductors are wired to a main circuit breaker or fuses. Another conductor is brought through the meter with the use of a jumper wire. It is connected to a neutral bar in the entrance panel. The electric outlet side of the main circuit breaker is called the load side. The inlet side of the circuit breaker that is wired to the meter is the line side. The line side to a fuse or circuit breaker is always energized with electrical power as long as it is being supplied by the power company. The load side of the main circuit breaker is connected to two conductors called the bus. The bus is the main supply to the branch circuit breakers line side. Figures 1-2 through 1-6 show actual photographs of the components mentioned in Fig. 1-1.
Fig. 1-2. Generating plant where electricity is produced and transmitted through the network.
Fig. 1-3. Substation where electricity is passed through step-down transformers before being sent through the local network.
Fig. 1-4. Typical step-down transformer found in the local neighborhood where the electrical voltage is dropped to the amount used by the consumer.
Fig. 1-5. Weatherproof service head where power company brings their transmission lines to the structure being supplied.
Fig. 1-6. Electric meter supplied by the power company, measures the amount of power being consumed within the structure.
Figure 1-7 shows a typical circuit breaker entrance panel with the cover removed. You can see the bus bars exposed where the circuit breakers were removed. The voltage/current flows from the bus through the circuit breaker of the branch circuit to the load (electrical consuming device-appliance-lighting). It then returns to the panel by way of the neutral, if the voltage is 120 volts. If the voltage is 240 volts, single phase, it will leave a branch circuit breaker on line one, flow to the load, and return to the panel on the load side of the same breaker on line two bus. The voltage from line one to neutral is 120 volts. The voltage from line two to neutral is 120 volts. The voltage from line one to line two is 240 volts. The current that the neutral carries in a three wire circuit is the difference between the currents in line one and line two.
Fig. 1-7. Typical circuit breaker entrance panel with cover removed.
The cold-water-pipe ground is wired to the neutral bar of the entrance panel. As long as the neutral is wired to the cold-water-pipe ground, the voltage of the neutral will be zero volts in respect to ground. The ground wire that connects to the load also connects to the cold-water ground at the panel.
The purpose of the service head (Fig. 1-5) is to keep water from entering the service-entrance conduit, meter, and main panel. The purpose of the service-entrance conduit is to protect the service-entrance conductors from physical damage and, in the case of fire, to protect against electrocution. Conduit is also used as a ground conductor. In many cases, branch circuit wiring leaves the main panel enclosed in conduit. Some types of conduit are rigid (hard wall), flexible, or thin wall. Romex is a wiring system using a conductor made of fiber or heavy plastic covering. In some areas, knob-and-tube type of wiring may still be seen (most areas have outlawed it).
The step-down transformer shown in Fig. 1-4 is normally mounted on the power pole. It is oil-filled and air-cooled. This type of transformer reduces voltages to the amount needed for customer purchase. Most homes today are a three-wire system. You can see them entering the structure. This type of arrangement allows the use of both 120- and 240-volt, single phase ac appliances. On some older homes built over 45 years ago, you might find two wires; this can only supply 120 volts ac, single-phase (only one line and the neutral was used). Referring to the schematic in Fig. 1-1, you can see that the wires from the pole feed the meter first. The meter is in series with the main breaker which is in series with all the branch circuit breakers of the entrance panel. The branch circuit breaker is the last over-current device that feeds an electrical load. In the case of 120 volts, the electrical flow is to the load and returns to the panel to the neutral. With 240 volts, electricity flows to the load through line one and returns to the branch breaker through line two.
Most changes or modifications in wiring deal with branch circuit wiring or feeder wiring. A feeder wire is a wire that connects between a branch breaker and a main panel breaker. You will find that branch circuit wiring can be many different sizes of wire as well as different amounts of conductors encased in the conduit. The size of the wire is determined by the maximum amperage consumption of the electrical load that the wire will supply.
For example, if you have a load (machine, appliance, etc.) that needs a current of 20 amps, according to the electrical code, you will need a #12 TW wire (the number of the wire refers to the American Wire Gauge). The lower the number, the larger the diameter becomes. The larger the diameter, the more current (load) the wire can carry safely. Table 1-1 shows an ampacity chart for copper conductors.
Table 1-1. Ampacity of Copper Conductors.
Due to the fact aluminum does not conduct as well as copper, aluminum wiring of the same gauge is rated to carry less current. Table 1-2 shows ampacity for aluminum conductors, and the difference between the two conductors is easily seen.
Table 1-2. Ampacity of Aluminum Conductors.
The diameter of conduit is dependent upon the region in which you are working. Consult the NEC (National Electrical Code) and the local electrical codes of your area. The amount of wires placed in a conduit is called the conductor fill. Some areas have a specified number of conductors allowed, depending upon the wire size. Other places allow as many conductors into a conduit as you can push through. Table 1-3 is a sample conductor fill chart that is used in some areas.
Table 1-3. Sample Conductor Fill Chart for EMT Used in Certain Areas Where Electrical Code is Still in Force.
The amount of current a wire can carry is dependent upon the type of metal the wire is made of, diameter of the wire, type of insulation covering the wire, and whether the wire is suspended in free air or inside an electrical conduit. High-voltage wiring normally has a small current. For this reason, the high voltage transmission lines on the power poles have small wiring.
You are charged for electricity by the amount you use. The unit of measure is watt-hours. Example: A one horsepower motor which is equal to 800 watts costs the same to operate at 120 volts as it does if you operate it at 240 volts. The 800 watt-hours is the same regardless of the voltage.
You pay for watt-hours (watts × time in hours). Some salesmen will attempt to sell a higher voltage machine of the same horsepower with the understanding that due to the lower current draw, the running cost will be less. This whole line of reasoning is false.
Figure 1-8 is a schematic of a three-phase power distribution panel and meter. Lines one, two, and three all have voltage when energized. Voltage can be 208, 240, 480, or higher. Note the delta-wired load on the left of the drawing and the star-wired load on the right of the drawing. All three-phase loads are wired either delta or star.
Fig. 1-8. Schematic of a three-phase distribution panel and meter.
Three-phase distribution uses three lines in which the peak voltage in each conductor is reached successively one-third of a cycle apart, 120 degrees of generator rotation. In effect there are three separate sine waves of potential (voltage) and three waves of current per cycle.
The current and voltage sine waves of a resistance circuit will be in step with each other. Normally, they have different wave heights, but the voltage wave intersects the amperage wave at 0, 180, and 360 degrees of phase time. When a coil (inductance) is in the circuit, the voltage sine wave will lead the current sine wave, or reach its peak value earlier in time.
With a capacitor in the circuit, the current will peak before the voltage, or the current wave will lead the voltage sine wave. An inductive circuit may have a capacitor placed in parallel to increase the power factor. With proper balance, the power factor can be corrected above nine-tenths; this process can also be reversed. A low power factor means the efficiency of the circuit is low and you end up paying for power that does no economic work.
Electricity is a form of energy that is a result of electrons in motion. The three important properties of electricity are voltage, current, and resistance. Voltage is electromotive force that pushes a flow of electrons, known as current, through a conductor or medium that has a resistance to slow the electrons that are being pushed.
Ohm’s law states that an electromotive force of one volt is required to push a current of one ampere through a resistance of one ohm. Voltage is a measure of electromotive force, potential, or electric pressure. Current is the volume of the flow of electrons being pushed along a conductor. Resistance is the ability of a substance or conductor to impede the flow of electrons being pushed by voltage. Power is the capacity of electricity to do work in a given time period and is expressed in watts. Letter symbols are as follows:
The triangle shown in Fig. 1-9 illustrates Ohm’s law. Use this triangle to find the unknown factor when two factors are known.
Fig. 1-9. Ohm’s law triangle.
Step 1—Cover the electrical value you want to find. The relationship of the formula becomes apparent. Example: If you want the value for E (voltage), cover E on the triangle.
Step 2—You can see I × R is visible. That is the formula. If you want to find I (current), cover I in the triangle. The formula relationship now would be 
to find I. To solve for R (resistance), cover R in the triangle. The formula relationship now becomes 
to find R. You will need these formulas often.
The two basic circuits in electricity are the series circuit and the parallel circuit. At the top of Fig. 1-10 a basic series circuit is shown. You can see there is only one path for the electricity to flow through from L1 to L2. If a device is placed into this type of circuit, the electrical energy will flow through it. In the bottom section of Fig. 1-10 an example of a basic parallel circuit is shown. You can see in this circuit, there are three different paths through which the electrical energy can flow at the same time. Both of these circuits are resistive as shown by the resistors labeled A, B, and C.
Fig. 1-10. (top) Series circuit; (bottom) Parallel circuit.
To find total resistance in the circuit use the following procedure. In the series circuit, just add the values of each resistor, and the total amount found is the total amount of resistance in the circuit. In the parallel circuit the relationship is different. The total resistance of a parallel circuit is usually smaller than the value of the smallest resistor in the circuit. In Fig. 1-11 you will find total resistance for the circuit to be smaller than the smallest resistor.
Fig. 1-11. Finding resistance totals in series and parallel circuits.
All general building wiring is rated at 600 volts ac. The current rating depends on the wire size (diameter of the wire) or the wire gauge, type of material (copper, aluminum), and type of insulation. Wiring is sized to handle the current consumption of the load. See Tables 1-1 and 1-2.
Conduit is a metal enclosure that protects the wiring and allows for a safe grounding. It is commonly called EMT (extruded metallic tubing). A nonmetallic conduit has been developed and accepted by the building industry which is accepted in many local codes, but of course it lacks the protection and grounding ability of the EMT. This plastic conduit is called PVC. In certain applications. Romex (a fibrous-covered wire) and cords may be used without conduit.
Grounding of PVC conduit is accomplished with the addition of a green-colored conductor that is used for grounding only. In the EMT system, grounding is accomplished by the metal of the conduit that is bonded to the grounding conduit to the cold water pipe.
Many small compressor/condenser sections are wired with a cord instead of conduit. Cords are rated at 250 volts or 600 volts. Check NEC and local codes for maximum allowable length of connecting cords. In some areas, the limit is 10 feet. Cords are coded to identify construction and application. As an example, cords may be coded SO, SJO, or SJ. SO cord has a heavy-duty, thick rubber covering with a jute filler surrounding the conductors. SJO cord is rated for medium duty with a medium thickness rubber covering and a combination of paper and jute surrounding the conductors. SJ cords are for light duty service. The rubber covering is very thin, and there is paper filler surrounding the conductors. Table 1-4 has ampacity ratings for cords.
Table 1-4. Wire Cords.
The following formula is used to find current when watts and volts are known. Example: 1600 watt compressor section at,
The cord or wire for the 120-volt condensing section will be #14 SO or #14 SJO. If conduit is being used, #14 TW wire can be used (copper) encased in one-half inch conduit. For a 240-volt condensing section, the cord would be #16 SO or #16 SJO. If conduit and wire is used, #14 TW (copper) and one-half inch conduit should be used. You can not use smaller gauge wire on this application. The smallest gauge wire allowed in general building is #14. If aluminum wiring is used, #12 TW should be used.
Table 1-5. Wire Coding Abbreviations.
