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Chapter 11

Chapter 11. APAD/ACPU A/C Control Systems. Optional AC Protection System. Overview. APAD- air conditioning protection and diagnostics system ACPU- air conditioning protection unit CM-813 – module used for TXV system CM-816 – module used only for orifice tube systems

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Chapter 11

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  1. Chapter 11 APAD/ACPU A/C Control Systems

  2. Optional AC Protection System

  3. Overview • APAD- air conditioning protection and diagnostics system • ACPU- air conditioning protection unit • CM-813 – module used for TXV system • CM-816 – module used only for orifice tube systems • Reduce maintenance costs and aid the technician in diagnostic work

  4. APAD Unit Mounted on Firewall Stand alone unit with LED blink codes

  5. APAD • Components: ECU, conventional evaporator thermostat, and two pressure switches • Module provides the only on/off output to compressor clutch and fan actuator control • Protects AC system components from total failures or self destruction caused by low or high refrigerant levels or electrical voltage problems • AC system not started until 15sec after engine start up (easier starting), will cycle in the winter for circulation of oil for lubrication • ACPU’s are the second generation of APAD units, they display messages in the dash of the vehicle

  6. Inputs and Outputs -High and low pressure switches are normally closed providing path to ground(semi-smart internal resistor for diagnostic use) -Evaporator thermostat wired in series with on/off switch used to prevent evaporator freeze up

  7. Description of Diagnostic Faults • See page 173 in the chapter…..

  8. Location of Pressure Switches

  9. Summary • APADs and ACPUs are not widely used. • Their purpose is to protect the compressor from self destruction. • Either blink codes or messages in the dash are displayed to aid the technician in diagnosing problems with the system

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