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 49, the reader should be able to: • • • • Identify the type of HVAC system being used on a vehicle Describe how dual-climate and rear airconditioning systems work Discuss vacuum and electric motor controls Explain how both heated and cooled air is blended 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: afterblow • ambient air temperature sensor • aspirator tube • automatic temperature control (ATC) system cabin filter discharge air temperature (DAT) sensor • dual-position actuator hybrid electric vehicle (HEV) photo diode • three-position actuator variable-position actuator 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 AIRFLOW MANAGEMENT All automatic heating, ventilation, and air­conditioning (HVAC)  systems use a combination of the following components to control  airflow into the passenger compartment: Vents Ducts Air doors (also called flap doors or valves) The use of these components allows the system to provide airflow  under the following conditions: Fresh outside air or recirculated air Air conditioning Defrost Heat Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 49–1 The three major portions of the A/C and heat system are air inlet, plenum, and air distribution The shaded portions show the paths of the four control doors 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 Typical settings for a manual or automatic air­conditioning system Heat Temperature set to the desired setting Air  intake—select  outside  air  (for  faster  heating,  select  recirculation for the first few minutes) Air conditioning set to off Set airflow to flow Fan speed to desired 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 Typical settings for a manual or automatic air­conditioning system Air­Conditioning Temperature set to the desired setting Air  intake—set  to  outside  air  (for  faster  cooling,  select  recirculation for the first few minutes) Airflow—select dash vents (also called panel vents) Air conditioning set to on Fan speed set to desired 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 Typical settings for a manual or automatic air­conditioning system Ventilation Temperature set to lowest temperature Air intake—select outside air Airflow—set to dash (panel) vents Air conditioning set to off Fan speed set to desired 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 Typical settings for a manual or automatic air­conditioning system Defogging or Defrosting the Inside of the windshield Temperature set to high temperature Air intake set to outside air Airflow set to windshield Fan speed set to desired 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 What is Afterblow? Afterblow is a term used to describe the operation of the blower motor after the ignition has been turned off The purpose of afterblow is to dry the evaporator to help prevent the formation of mold and mildew in the evaporator case The operation of the blower motor after the ignition is turned off has created some customer complaints Check service information to be sure that the condition is normal or not on the vehicle being investigated For example, in a typical General Motors system, the following conditions must be met for afterblow to occur: The engine has been off for 30 minutes The outside air temperature is 70°F (21°C) or higher The battery voltage is 12 volts or higher If the above conditions exist, the afterblow is commanded to be on for 20 seconds, off for 10 seconds, and back on for another 20 seconds 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 VACUUM CONTROL CIRCUITS Vacuum control circuits use  vacuum created in the intake  manifold of the engine.  Because vacuum decreases close to zero during heavy  acceleration, a vacuum  accumulator is used to store vacuum during short  periods of acceleration.  Figure 49–5 With no vacuum signal, the spring extends the actuator shaft to place the door in a certain position (top) A vacuum signal pulls the shaft inward and moves the door to the other position (bottom) 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 ELECTRIC SERVOMOTOR CIRCUITS Most HVAC systems use electric motors to move valves and doors.  Each servomotor contains a feedback potentiometer, which is used  by the air conditioning control unit to indicate the actual position  of the valve or door If the commanded position and the actual position are not the same,  then most systems are designed to store a diagnostic trouble code  indicating which door is out of calibration See Figures 49–6 and 49­7 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 49–6 Three electric actuators can be easily seen on this demonstration unit However, accessing these actuators in a vehicle can be difficult Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 49–7 The feedback circuit signals the AC control unit with the blend door position ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 BLOWER MOTOR CONTROL Blower motors are used to move air. The air is directed by the  doors of the HVAC system Most blower motors use resistors to control speed of the motors  by dropping the amount of current flow through the motor at the  lower speed. The resistor lowers voltage and current to the motor The control allows full system voltage to be applied to the motor  during high­speed operation. The blower motor resistor is always  located in the plenum near the blower motor so that airflow past  the resistor can help keep it cool See Figures 49–8 and 49–9 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 49–8 A typical blower motor assembly with attached squirrel cage blower A replacement motor does not include the squirrel cage blower so it needs to be switched to the replacement Figure 49–9 A “credit card” resistor used in the rear blower assembly in a Dodge minivan 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 DUAL-ZONE AIR CLIMATE CONTROL Dual­zone climate controls allow the driver and the passenger to  select different temperatures, as much as a 30°F (17°C) difference In a dual­zone climate control system, the ducts and airflow are  split and two air mix doors are used, with each door being  controlled by its own actuator See Figure 49–10 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 49–10 A dual climate control system showing the airflow and how it splits 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 REAR AIR-CONDITIONING SYSTEM Many larger trucks, vans, and sport utility vehicles (SUVs) are  equipped with rear heat and air­conditioning units. Many vehicles  are equipped with ducts that route heated or cooled air to rear­seat  passengers.  Figure 49–11 A typical dualzone climate control panel showing left and right side temperature control levers 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 However, many larger vehicles require a separate heater core and  air­conditioner evaporator in the rear to provide adequate heating  and cooling. Most rear HVAC systems include the following  components: Larger capacity air­conditioning compressor Second evaporator at rear of the vehicle Second heater core at rear of the vehicle Second blower motor and control  Lines and fittings connecting front heater and air­conditioning components to the rear system Rear controls for speed & temperature  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 49–12 Heated or cooled air is supplied to the rear seat passengers of most vehicles through ducts that run under the front seats ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 49–13 A sticker on a vehicle equipped with rear heat and air-conditioning warning that a special service procedure is needed when replacing engine coolant 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 RECIRCULATION OPERATION When recirculation is selected, about 90% of the air is drawn from  the passenger compartment and the other 10% is drawn from  outside air. The purpose is to speed up the cooling of the inside of  the vehicle However, the body control module may also select recirculation  operation if the high­side air­conditioning system pressures exceed  320 psi (2,200 kPa) to help lower the high­side pressure using  cooler inside air through the evaporator This condition should not normally occur, but if it does, this could  cause a customer concern because the blower noise is greatly  increased in the recirculation position 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 HYBRID ELECTRIC VEHICLE HEATING AND COOLING SYSTEMS Hybrid electric vehicle (HEV) systems need to be different than  conventional systems because the engine stops when at idle if the  engine is warm. As a result, the engine­driven air­conditioning  compressor will also stop. To allow idle­stop mode and still provide  air conditioning, several methods are used: Idle­stop mode is disabled if max cooling is selected Honda uses a hybrid compressor which has a smaller  capacity, operated by an electric motor, powered by the high­ voltage (HV) batteries Toyota uses an air­conditioning compressor entirely driven by  the HV batteries, capable of providing cooling under all  conditions, including when the engine is not operating 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 HVAC systems are designed to be able to deliver airflow to  the windshield for defogging or defrosting as well as to the  floor or dash vents HVAC systems are designed to use outside air, recirculated  air, or a combination of the two Sensors used in automotive air­conditioning systems include  outside air temperature (OAT), inside vehicle temperature,  discharge air temperature (DAT), evaporator outlet  temperature, and sunload sensors 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.) Actuators include dual­position, three­position, and variable  position actuators Most valves and airflow doors are electrically driven by  motors and a feedback potentiometer Rear air­conditioning systems use a second heater core and  evaporator at the rear of the vehicle Hybrid electric vehicles use a variety of components and  systems to be able to provide air conditioning under idle­stop  conditions 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