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Automatic A/c-Heater Systems: Overview Lexus LX J100

Automatic HVAC System 1 illustration ~351 words

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WARNINGTo avoid injury from accidental air bag deployment, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG SYSTEM SAFETY article in GENERAL SERVICING.
CAUTIONWhen battery is disconnected, radio will go into anti-theft protection mode. Obtain radio anti-theft protection code from owner prior to servicing vehicle.

Note. Vehicle is equipped with both a front A/C Electronic Control Unit (ECU) and rear A/C amplifier. Front A/C ECU may also be referred to as front A/C amplifier.

Front A/C ECU, automatically controls all A/C and heating functions. Manual controls allow driver to select air distribution mode and desired temperature. In addition to normal A/C system components, automatic A/C system includes various amplifiers, servomotors, controls, and sensors. (Scheme 21) An exhaust gas sensor is used to change from fresh to recirculated intake air when exhaust gases are sensed from another vehicle.

Rear A/C functions are controlled separately by an independent rear A/C control panel. Rear A/C has a separate A/C amplifier that allows automatic operation to be selected on rear A/C control panel. A separate rear in-vehicle temperature sensor and rear evaporator temperature sensor monitor rear A/C system and send signals to rear A/C amplifier. (Scheme 21)

Scheme 21

Scheme 21
Scheme 21

No Blower Motor Operation

  1. Check ACC power source circuit. See «ACC POWER SOURCE CIRCUIT»(ref-98895-S02437621282001060500000) under SYSTEM TESTS.
  2. Check heater main relay. See «HEATER MAIN RELAY»(ref-98895-S41559554082001060500000) under COMPONENT TESTS.
  3. Check blower motor circuit. See «BLOWER MOTOR CIRCUIT»(ref-98895-S32395191622001060500000) under SYSTEM TESTS.
  4. Check A/C Electronic Control Unit (ECU). See «FRONT A/C ECU (W/O NAVIGATION SYSTEM)»(ref-98895-S41625521632001060500000) or «FRONT A/C ECU (W/ NAVIGATION SYSTEM)»(ref-98895-S30481195422001071600000) under SYSTEM TESTS.
  5. Check front blower motor control relay. See «RELAYS»(ref-98895-S31781469152001072000000) under COMPONENT TESTS.
  1. Check ACC power source circuit. See «ACC POWER SOURCE CIRCUIT»(ref-98895-S02437621282001060500000) under SYSTEM TESTS.
  2. Check rear heater main relay. See «RELAYS»(ref-98895-S31781469152001072000000) under COMPONENT TESTS.
  3. Check rear blower motor. See «BLOWER MOTOR»(ref-98895-S33075614572001072000000) under COMPONENT TESTS.
  4. Check rear blower motor power transistor (heater or cooler). See «REAR BLOWER MOTOR POWER TRANSISTORS»(ref-98895-S38654375432001060500000) under COMPONENT TESTS.
  5. Check rear A/C amplifier. See «REAR A/C AMPLIFIER»(ref-98895-S14713355932001060500000) under SYSTEM TESTS.

Rear Expansion Magnetic Valve Operation Check

Check air passage though expansion valve with and without battery voltage applied. Using a fused jumper wire, connect battery voltage across magnetic valve connector terminals. With battery voltage applied, air passage should be open. With battery voltage removed, air passage should be closed. Replace expansion valve with magnetic valve if operation is not as specified.

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