FIGURE 14-1 Electrical pressure is measured in volts; refrigerant pressure is measured in pounds per square inch (a). Electrical current flow is measured in amps; refrigerant flow is measured by volume (b). Electrical resistance causes a voltage drop; resistance in an A/C system causes a pressure drop (c).

FIGURE 14-1 (CONTINUED) Electrical pressure is measured in volts; refrigerant pressure is measured in pounds per square inch (a). Electrical current flow is measured in amps; refrigerant flow is measured by volume (b). Electrical resistance causes a voltage drop; resistance in an A/C system causes a pressure drop (c).

FIGURE 14-2 An electric circuit must be complete for current to flow FIGURE 14-2 An electric circuit must be complete for current to flow. Circuits are shown in the form of a diagram (a) or schematic (b).

FIGURE 14-3 A series circuit (a) and a parallel circuit (b).

FIGURE 14-4 These symbols are used to show the components of an A/C electrical system. (Courtesy of Everco Industries)

FIGURE 14-5 This A/C electrical circuit has a power source (a); fuses to protect the circuit (b); switches to control the circuit (c); wires connecting each of the components (d); and two outputs: the blower motor and the compressor clutch (e).

FIGURE 14-6 Circuit protection can be fuses with tubular or flat blade connections (a), a circuit breaker (b and c), or a fusible line (d). (Courtesy of Chrysler LLC)

FIGURE 14-6 (CONTINUED) Circuit protection can be fuses with tubular or flat blade connections (a), a circuit breaker (b and c), or a fusible line (d). (Courtesy of Chrysler LLC)

FIGURE 14-7 A simple switch can be normally open or normally closed (a). Relays use a magnetic coil to close or open switch contacts (b).

FIGURE 14-8 Electrical wire is sized by gauge sizes, American wire gauge (AWG) (a). Wire colors with stripes, dots, or hash marks are used to identify particular wires (b). (Courtesy of Everco Industries)

FIGURE 14-9 Insulated wires are used to conduct electricity to the clutch coil. The metal of the engine forms the ground circuit to complete the circuit back to the battery. A circuit is shown in a diagram (a) and a schematic (b).

FIGURE 14-10 The strength of a magnetic coil is determined by multiplying the number of wire turns by the current flow. (Courtesy of Warner Electric)

FIGURE 14-11 This diode (a) is part of the clutch coil wire harness FIGURE 14-11 This diode (a) is part of the clutch coil wire harness. The zener (b) diode at the clutch coil connector prevents a high voltage spike when the clutch releases. (b courtesy of Everco Industries)

FIGURE 14-12 Most of the control components of an ATC system are solid-state electronic devices—diodes, thermistors, and transistors. (Courtesy of Chrysler LLC)

FIGURE 14-13 This pressure sensor is a transducer that changes high-side pressure into an electrical signal for an ECM input.

FIGURE 14-14 The resistance value of the in-car sensor or ambient sensor is inversely related to the temperature. As the temperature increases, the resistance decreases.

FIGURE 14-15 This electronic control head receives B + power through terminal 1 and input through the other terminals shown at the left. It controls the components shown at the right. (Courtesy of Chrysler LLC)

FIGURE 14-16 With the ignition switch on, pressing the AUTO and REC switch at the same time will enter a DTC check on this vehicle (a). A blink code (b) will be indicated by flashes of the indicator lights. (Provided courtesy of Toyota Motor Sales USA, Inc.)

FIGURE 14-17 Modern electrical components use weather-tight connectors with locks to keep the contacts clean and tight (a). Releasing the latching tab allows the connector to be removed (b).

FIGURE 14-18 The multiplex between the BCM and PCM is the path for each to send messages or signals to each other as well as the transaxle control module (TCM), electromechanical instrument cluster (MIC), air-bag control module (ACM), and data link connector (DLC). (Courtesy of Chrysler LLC)

FIGURE 14-19 This power distribution center contains the relays and most of the fuses for this vehicle. Note the inside of the cover (left) has a legend to identify the relays and fuses.

FIGURE 14-20 This A/C compressor clutch relay is controlled by the PCM FIGURE 14-20 This A/C compressor clutch relay is controlled by the PCM. Note that the radiator fan motor uses a solid-state relay that is also controlled by the PCM. (Courtesy of Chrysler LLC)

FIGURE 14-21 The A/C request goes from the HVAC module to the PCM, and if all conditions are correct, the PCM activates the A/C relay to turn the A/C on.

FIGURE 14-22 A blower with hot-side switching (a) and groundside switching (b). Note the relationship of the blower switch and resistors and the blower motor, B +, and ground connection.

FIGURE 14-23 Three relays (at right center) control the current flow for the three blower speeds. Note that the flow for low and medium speeds passes through a resistor.

FIGURE 14-24 This system uses three relays to provide four blower speeds. Note that the relays are energized by the A/C controller in the proper order to provide those speeds.

FIGURE 14-25 The current for this two-fan circuit is controlled by two relays, which are in turn controlled by the PCM.

FIGURE 14-26 The inverter converts dc voltage from the battery to high voltage (HV) ac for the drive motor and A/C compressor. Note the cooling components.

FIGURE 14-27 A high-voltage compressor is powered by electricity (a); note the electrical harness. It is mounted on the engine to reduce noise (b).

FIGURE 14-28 An open circuit is a break in the circuit that will stop the current flow (a). Corroded or loose connections will cause high resistance that will reduce the current flow (b). (Courtesy of Chrysler LLC)

FIGURE 14-28 (CONTINUED) An open circuit is a break in the circuit that will stop the current flow (a). Corroded or loose connections will cause high resistance that will reduce the current flow (b). (Courtesy of Chrysler LLC)

FIGURE 14-29 A short circuit is often a wire-to-wire connection that can reduce magnetic coil strength or allow current to flow to the wrong circuit (a). It can also be a short to ground (b). (Courtesy of Chrysler LLC)

FIGURE 14-30 A ground or short-to-ground circuit occurs when damage to the insulation allows an electrical path to the metal of the vehicle (a). It can occur at a wire or inside a component (b). (Courtesy of Chrysler LLC)

FIGURE 14-31 Jumper wires can often be used to bypass portions of a circuit to determine where the problem is located. This jumper wire has a fuse to limit the current flow (a). If the lights illuminate with the jumper wire installed, the problem is the fuse, switch, or wires to the battery (b).

FIGURE 14-32 A self-powered test light includes a battery and can be used to check for continuity (a). An ordinary nonpowered test light (b) can be used to determine if a point in a circuit has voltage (c).

FIGURE 14-32 (CONTINUED) A self-powered test light includes a battery and can be used to check for continuity (a). An ordinary nonpowered test light (b) can be used to determine if a point in a circuit has voltage (c).

FIGURE 14-33 A test light connects the motor to B while the other motor connector is grounded. The test light should illuminate and blink off as the motor shaft is rotated.

FIGURE 14-34 An analog (a) and a digital (b) multimeter FIGURE 14-34 An analog (a) and a digital (b) multimeter. The digital display and bar graph are both displaying 9.37 volts (c). (b and c courtesy of OTC Division, SPX Corporation)

FIGURE 14-35 Extreme care should be used when testing components that display this ESD symbol.

FIGURE 14-36 This modernized version of Ohm’s law shows the relationship between volts, current (amps), and resistance.

FIGURE 14-37 Voltage is measured by connecting one voltmeter lead (normally the negative) to ground and probing the wire connections with the other lead (a); different readings indicate a voltage drop. Voltage drop can also be checked at each component (b).

FIGURE 14-37 (CONTINUED) Voltage is measured by connecting one voltmeter lead (normally the negative) to ground and probing the wire connections with the other lead (a); different readings indicate a voltage drop. Voltage drop can also be checked at each component (b).

FIGURE 14-38 This meter is connected to measure the voltage drop across the resistor. (Courtesy of Fluke; reproduced with permission)

FIGURE 14-39 Voltage drops across resistors can be measured indirectly (a) or directly (b). Source voltage at the input side minus the indirect measurement will equal the direct measurement.

FIGURE 14-39 (CONTINUED) Voltage drops across resistors can be measured indirectly (a) or directly (b). Source voltage at the input side minus the indirect measurement will equal the direct measurement.

FIGURE 14-40 This fuse check shows a good voltage reading; the reading should be the same at both fuse contact points. The negative (–) voltmeter is connected to a good ground.

FIGURE 14-41 A digital multimeter being used to measure resistance FIGURE 14-41 A digital multimeter being used to measure resistance. Be sure to turn off or disconnect the electrical power to the circuit when using ohmmeter functions. (Courtesy of Fluke; reproduced with permission)

FIGURE 14-42 Attaching one of the ohmmeter leads to the coil housing checks for a ground (a). Connecting the two leads of the ohmmeter to the two leads of a clutch coil measures resistance and checks for shorts (b). The resistance reading should match the manufacturer’s specification; the ground reading should be 0.(Courtesy of Warner Electric)

FIGURE 14-43 A digital multimeter being used to measure current flow (a). A transformer probe can be used to check current flow without breaking the circuit (b). (Courtesy of Fluke; reproduced with permission)

FIGURE 14-43 (CONTINUED) A digital multimeter being used to measure current flow (a). A transformer probe can be used to check current flow without breaking the circuit (b). (Courtesy of Fluke; reproduced with permission)

FIGURE 14-44 The jaws of the amp probe are around the wire for clutch power, and the probe is connected to the DMM. The clutch is drawing 2.85 amps, which should be normal.

FIGURE 14-45 A blown fuse has been modified by soldering a short wire to each test point (a). Replacing a circuit fuse with the modified fuse allows an easy location to check the circuit’s current flow (b).

FIGURE 14-46 This diagnostic link connector (DLC) is at the bottom of the instrument panel (a). A scan tool can be connected to the DLC, which allows it to connect to the vehicle’s controls (b). (b courtesy of MACS)

FIGURE 14-47 The DRB III is a scan tool that is dedicated to DaimlerChrysler vehicles (a). It can be used to read various functions (b) or perform various service operations. (Courtesy of Chrysler LLC)

FIGURE 14-47 (CONTINUED) The DRB III is a scan tool that is dedicated to DaimlerChrysler vehicles (a). It can be used to read various functions (b) or perform various service operations. (Courtesy of Chrysler LLC)

FIGURE 14-48 With the ignition switch on and the fan switch off, pressing on the recirculation control switch will cause this vehicle to enter self-diagnosis. The DTC can be read from the blinking of the recirculation indicator light. The pattern for DTC 2 is shown. (Courtesy of American Honda Motor Co., Inc.)

FIGURE 14-49 The first letter of an OBD-II code identifies the function of the fault code area; body faults begin with the letter B. The first digit indicates if the DTC is generic or manufacturer specific. The second digit indicates the power-train system, and the last two digits indicate the fault.

FIGURE 14-50 A terminal repair set FIGURE 14-50 A terminal repair set. It includes replacement connectors and special pliers to install them, as well as a group of tools to remove terminals from weather-tight connectors. (Courtesy of Kent-Moore)

FIGURE 14-51 A terminal is usually pushed into a weather-tight connector until it locks into place (a). A pick tool is used to unlock the terminal for removal. (Reprinted with permission of General Motors Corporation.)

FIGURE 14-52 A wire stripping and crimping tool (a) FIGURE 14-52 A wire stripping and crimping tool (a). The stripping area is used to cut the insulation and pull it off the wire (b).

FIGURE 14-53 A splice can be made quickly by crimping a wire connector to the two wires.

FIGURE 14-54 A wire splice can be made by removing insulation from the two wires (left), sliding the two ends together (center), and twisting them so they stay together while they are soldered (a). The connection is then soldered using rosin-core solder for security (b).

FIGURE 14-55 A wire splice should be insulated using shrink tubing (a) or by wrapping it tightly with plastic tape (b).