chap44 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 44, the reader should be able to: • • • • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “G” (Horn and Wiper/Washer Diagnosis and Repair) and content area “H” (Accessories Diagnosis and Repair) Describe how the horn operates List the components of a wiper circuit Explain how the blower motor can run at different speeds Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: horns • pulse wipers rain sense module (RSM) • rain-sense wipers series-wound field • shunt field variable-delay wipers windshield wipers Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Electrical accessories provide comfort and assistance to the driver and passengers The growing list of electrical accessories makes this an area of much concern to vehicle owners and service technicians Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 HORNS Horns are devices that emit a loud sound and vehicles have one or two horns Figure 44–1 The two horns on this vehicle were finally located under the front bumper They were not visible until the vehicle was hoisted When two are used, each has a different tone when operated separately, yet sound combines when both are operated Automotive horns are usually wired directly to battery voltage from the fuse panel A majority, except for most Fords, utilize a horn relay Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 With a relay, when the horn button on the steering wheel or column completes a circuit to ground that closes a relay, current required by the horn then travels from the relay to the horn Some older systems not use a relay, and current is supplied directly to the horn through a switch in the steering column The horn circuit includes an armature and contacts attached to a diaphragm The armature causes the diaphragm to vibrate audibly Figure 44–2 A typical horn circuit Note that the horn button completes the ground circuit for the relay Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 A vehicle horn is an actuator that converts an electrical signal to sound The sound created by the diaphragm is magnified as it travels through a trumpet attached to the diaphragm chamber Most horn systems typically use one or two horns, but some have up to four Those with multiple horns use both high- and low-pitch units to achieve a harmonious tone Only a high-pitched unit is used in single-horn applications The horn assembly is marked with “H” or “L” for pitch identification Horns are manufactured in several different tones or frequencies ranging between 1,800 and 3,550 hertz Vehicle manufacturers can select from various horn tones for a particular vehicle sound Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Horn System Diagnosis There are three types of horn failure: No horn operation Intermittent operation Constant operation If a horn does not operate at all, check for: Burned fuse or fusible link Open circuit Defective horn Faulty relay Defective horn switch If a horn operates intermittently, check for: Loose contact at the switch Loose, frayed, or broken wires Defective relay Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 A horn that sounds continuously and cannot be shut off is caused by horn switch contacts that are stuck closed, or a short-to-ground on the control circuit This may be the result of a defective horn switch or a faulty relay Stuck relay contacts keep the circuit complete so the horn sounds constantly Disconnect the horn and check continuity through the horn switch and relay to locate the source of the problem To help determine the cause of an inoperative horn, use a jumper wire and connect one end to the positive post of the battery and the other end to the wire terminal of the horn itself Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 If the horn works, the problem is in the circuit supplying current to the horn If the horn does not work, the horn itself could be defective or the mounting bracket may not be providing a good ground If a replacement horn is required, attempt to use a horn of the same tone as the original The tone is usually indicated by a number or letter stamped on the body of the horn Horn Service When a horn malfunctions, circuit tests are made to determine if the horn, relay, switch, or wiring is the source of the failure Typically, a digital multimeter (DMM) is used to perform voltage drop and continuity checks to isolate the failure Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Rain-Sense Wiper Diagnosis and Service If there is a complaint about the rain-sense wipers not functioning correctly, check the owner’s manual to be sure that they are properly set and adjusted Also, verify that the windshield wipers are functioning correctly on all speeds before diagnosing the rain-sensor circuits Always follow the vehicle manufacturer’s recommended diagnosis and testing procedures Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 BLOWER-MOTOR OPERATION The same blower motor moves air inside the vehicle for air conditioning, heat, and defrosting or defogging The fan switch controls the path that the current follows to the blower motor The motor is usually a permanent-magnet, one-speed motor that operates at its maximum speed with full battery voltage The switch gets current from the fuse panel with the ignition switch on, then directs full battery voltage to the blower motor for high speed and to the blower motor through resistors for lower speeds NOTE: Always use good-quality windshield washer fluid from a closed container to prevent contaminated fluid from damaging the washer pump Radiator antifreeze (ethylene glycol) should never be used in any windshield wiper system Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 44–20 A typical squirrel cage blower motor A replacement blower motor usually does not come equipped with the squirrel cage blower, so it has to be switched from the old motor Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 44–21 Typical blower motor resistors used to control blower motor speed Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 44–22 A brushless DC motor that uses the body computer to control the speed (Courtesy of Sammy’s Auto Service, Inc.) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 BLOWER MOTOR DIAGNOSIS If the blower motor does not operate at any speed, the problem could be any of the following: A defective ground wire or ground wire connection A defective blower motor (not repairable; must be replaced) An open circuit in the power-side circuit, including fuse, wiring, or fan switch If the blower works on lower speeds but not on high speed, the problem is usually an inline fuse or high-speed relay that controls the heavy current flow for high-speed operation The high-speed fuse or relay usually fails as a result of internal blower motor bushing wear, which causes excessive resistance to motor rotation Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 At slow blower speeds, the resistance is not as noticeable and the blower operates normally The blower motor is a sealed unit, and if defective, must be replaced as a unit If the blower motor operates normally at high speed but not at any of the lower speeds, the problem could be melted wire resistors or a defective switch See Figure 44–23 The blower motor can be tested using a clamp-on DC ammeter, as shown in Figure 44–24 Most blower motors not draw more than 15 A on high speed A worn or defective motor usually draws more current than normal and could damage the blower motor resistors or blow a fuse if not replaced Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 44–23 A typical blower motor circuit with four speeds The three lowest fan speeds (low, medium-low and medium-high) use the blower motor resistors to drop the voltage to the motor and reduce current to the motor On high, resistors are bypassed The “high” position on the fan switch energizes a relay, which supplies current for the blower on high through a fusible link Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 44–24 Using a mini AC/DC clamp-on multimeter to measure the current draw of a blower motor Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The 20 Ampere Fuse Test Most blower motors operate at about 12 amps on high speed If the bushings (bearings) on the armature of the motor become worn or dry, the motor turns more slowly Because a motor also produces counter EMF, or CEMF, as it spins, a slower-turning motor will actually draw more amps than a fast-spinning motor If a blower motor draws too many amps, the resistors or the electronic circuit controlling the blower motor can fail Testing actual current draw of the motor is sometimes difficult because amperage often exceeds the permissible amount for most digital meters One test recommended by GM is to unplug the power lead to the motor (retain the ground on the motor) and use a fused jumper lead with one end connected to the battery’s positive terminal and the other end to the motor terminal Use a 20-am fuse in the test lead, and operate the motor several minutes If the motor draws over 20 amps, the fuse will blow Some experts recommend a 15-amp fuse If the 15-amp fuse blows and the 20-amp fuse doesn’t, you know the approximate motor current draw Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRICAL ACCESSORY SYMPTOM GUIDE The following list will assist technicians in troubleshooting electrical accessory systems See the chart on Page 503 of your textbook Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 NOTE: If the high-speed fuse blows a second time, check the current draw of the motor and replace the blower motor if the current draw is above specifications Check for possible normal operation if the rearwindow defogger is not in operation; some vehicles electrically prevent simultaneous operation of the high-speed blower and rear-window defogger to help reduce the electrical loads Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Horn frequency can range from 1,800 to 3,550 Hz Most horn circuits use a relay, and the current through the relay coil is controlled by the horn switch Most windshield wipers use a three-brush, two-speed motor Windshield washer diagnosis includes checking the pump both electrically and mechanically for proper operation Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Most blower motors use resistors wired in series to control blower motor speed A good blower motor should draw less than 20 amperes Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458