Print Reading for HVACR, 1st Edition Page 210 (228 of 368)

210 Print Reading for HVACR
Copyright Goodheart-Willcox Co., Inc.
B
R1
R1
R2
R2
R3
R3
L1
N
SW
A
R1
R1
R2
R2
R3
R3
L1
N
SW
L1 N L1 N
R1
SW
R2
R3
R3
Bulb
C D
R1
R2
Goodheart-Willcox Publisher
Figure 9-12. A—Highlighting all of the lines directly connected to L1. B—Highlighting
all of the lines directly connected to N in a different color. C—The rails of the ladder
diagram are represented by the two different colors used to represent Line 1 and
Neutral lines. D—The uncolored line segments represent the individual circuits that
make up the rungs on the ladder diagram.

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210 Print Reading for HVACR
Copyright Goodheart-Willcox Co., Inc.
B
R1
R1
R2
R2
R3
R3
L1
N
SW
A
R1
R1
R2
R2
R3
R3
L1
N
SW
L1 N L1 N
R1
SW
R2
R3
R3
Bulb
C D
R1
R2
Goodheart-Willcox Publisher
Figure 9-12. A—Highlighting all of the lines directly connected to L1. B—Highlighting
all of the lines directly connected to N in a different color. C—The rails of the ladder
diagram are represented by the two different colors used to represent Line 1 and
Neutral lines. D—The uncolored line segments represent the individual circuits that
make up the rungs on the ladder diagram.

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Chapter 9 Electrical Wiring Diagram Basics 209
Copyright Goodheart-Willcox Co., Inc.
1. Color all the lines connected to L1 one color, Figure 9-12A. Only wires
that are electrically the same L1 should be colored. Once an electrical
component, such as a switch or load, has been reached, the line stops.
2. Color all the lines connected to N a different color, Figure 9-12B.
The red and green color-coded lines now represent the rails of the
ladder, with the red line representing Line 1 on the left, and green
representing N on the right, Figure 9-12C.
3. Add the fi rst remaining, uncolored line, SW and R1 coil as the fi rst
rung of the ladder diagram. Each line segment that begins at one
color and ends at the other, is one rung on the ladder, Figure 9-12D.
4. Add the line with R1 contacts and an R2 coil to the second rung of
the ladder diagram.
5. Add the line with R2 contacts and an R3 coil to the third rung of the
ladder diagram.
6. Add the line with R3 contacts and the light bulb to the fi nal rung of
the ladder diagram.
By adding each of these rungs to the diagram, the completed ladder diagram
is created. From this completed diagram, it can be seen that the switch,
when closed, energizes the coil of relay 1. This causes the contacts of relay 1
to close, energizing the coil of relay 2. This causes the contacts of relay 2
to close, energizing the coil of relay 3. This causes the contacts of relay 3
to close, energizing the light bulb. Although the process of converting a
schematic diagram to a ladder diagram takes practice, the result is worth the
effort. Note that the order of rungs on the ladder diagram is not important.
9.2.5 Converting Schematic Diagrams to Ladder Diagrams
Not all equipment manufacturers provide ladder diagrams with their
equipment. However, a schematic diagram can be easily converted to a
ladder diagram for troubleshooting purposes.
Converting Schematic Diagrams
to Ladder Diagrams
One of the easiest ways to accomplish this is to use two different-color
highlighters to identify the power supply to the circuit. Consider the
schematic diagram in Figure 9-11.
Procedure
R1
R1
R2
R2
R3
R3
L1
N
SW
Goodheart-Willcox Publisher
Figure 9-11. An example of a schematic wiring diagram to be converted into a ladder diagram.

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Chapter 9 Electrical Wiring Diagram Basics 211
Copyright Goodheart-Willcox Co., Inc.
9.3 Basic Window Air-Conditioning Unit Wiring
Diagrams
The window-type unit is a plug-in appliance mounted in the window.
This unit is similar in electrical wiring confi guration to through-the-wall
units, but does not have solid sides and is not installed through the wall.
Window units are considered more of a temporary installation, while
through-the-wall unit installations require structural modifi cations. The
following factors make electrical diagrams for window and through-the-
wall units easier to understand:
■ There is typically only one fan motor on window and through-the-
wall units. The fan motor has two shafts—one to turn the condenser
fan blade and one to turn the evaporator blower.
■ The thermostat and other associated controls are all line voltage
devices. There is no control transformer.
■ No fi eld-installed wiring is required.
■ The unit has few control devices. This makes the circuits relatively
easy to trace out and evaluate.
The wiring diagram for a typical window unit is shown in Figure 9-13.
A legend is provided, denoting the electrical connections made in each mode
of system operation. Thus, these diagrams are easy to follow even though
the internal workings of the switch are not shown. For example, if the selec-
tor switch is set to the HIGH FAN position, contacts L1-1 will close on the
switch. This action causes the fan to operate at high speed, as indicated by
the current path highlighted in Figure 9-14A. If the selector switch is set to
the HIGH COOL position, contacts L1-1-C will close on the switch, which
causes the high-speed fan and the compressor to operate, Figure 9-14B.
L1
1
2
3
C
Thermostat
Run capacitor
Run capacitor
Compressor
C
S
R
Fan motor
HIGH
MEDIUM
LOW
L1 N
Selector
switch
Switch positions
Off None
Low fan L1-3
Medium fan
High fan
Low cool
Medium cool
High cool
Common
L1-2
L1-1
L1-C-3
L1-C-2
L1-C-1 Overload
Goodheart-Willcox Publisher
Figure 9-13. The schematic wiring diagram of a typical window or through-the-wall air-
conditioning unit.

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