APAD/ACPU A/C Control Systems

1. CHAPTER APAD/ACPU A/C Control Systems 11 Instructor Name:(Your Name)

2. Learning Objectives • Explain how an APAD system improves the reliability of an A/C system. • Describe the functions of an APAD system. • List the inputs of an APAD or ACPU module. • List the outputs of an APAD or ACPU module. • Explain what occurs when the control module senses low system refrigerant pressure. • Explain what occurs when the control module senses a complete loss of refrigerant.

3. Learning Objectives (continued) • Explain what occurs when the control module senses high refrigerant pressure. • Explain what occurs when the control module senses low supply voltage. • Explain what occurs when the control module senses high system voltage. • Locate the diagnostic information in order to interpret blink codes the module can display.

4. Learning Objectives (continued) • List in order of priority, the faults the APAD control module can display. • Describe how an ACPU communicates faults and where those faults are displayed.

5. Volvo APADs Unit Mounted on Truck’s Firewall

6. Electronically Managed HVAC Systems • APAD- Air Conditioning Protection and Diagnostics. • ACPU- Air Conditioning Protection Unit.

7. Advantages of APAD • Actively monitoring system conditions. • Controls the A/C compressor. • Controls the engine cooling fan. • Does not allow operation in unstable or self-destructive modes. • Provides diagnostic codes to technician for service and troubleshooting.

8. Functions of APAD • Acts as system controller. • Provides outputs to A/C components. • Receives inputs for A/C system switches. • Provides blink codes for system diagnostics. • Provides diagnostic communication via J1587 data bus. • Interfaces with electronically controlled diesel engines. • Places limits on dynamic responses of system to certain operating conditions.

9. Functions of APAD (continued) • Helps reduce A/C operating costs by: • Prevent rapid compressor cycling. • Prevent rapid cycling of engine fan at idle. • Prevent compressor clutch slippage due to low voltage. • Relieve stress on starting system by holding off A/C until 15 seconds after startup. • Lubricate system by cycling compressor for 15 seconds after start up. • Show system fault codes.

10. Inputs and Outputs, Line diagram

11. Inputs for ACPU-813 Controller • HPx- High pressure switch • LPx- Low pressure switch • TStat- Evaporator thermostat switch

12. Pressure Switch

13. Pressure Switch on Vehicle

14. Outputs for ACPU CM813 Controller • A/C Drive (compressor clutch drive) • Fan (Engine fan actuator) • Diagnostic LEDs

15. APADS Rules for Compressor Control (CM-813) • Compressor never turns on until 15 seconds after ignition switch is turned on. • Module initially ignores inputs, turns on compressor for 15 seconds after 15 seconds engagement time. If inputs are out of bounds compressor is shut down. • The compressor cycle rate is limited to one time every 15 seconds. • The Tstat is the primary controller.

16. APADS Rules for Compressor Control CM-813 (continued) • In a high pressure condition the compressor is allowed to stay on an algorithmically determined time, no more than 10 seconds. Compressor will restart after HPx resets and rule 3 is satisfied. • In a low pressure condition the compressor is shut down. Compressor will restart after LPx resets and rules 3 and 8 are satisfied.

17. APADS Rules for Compressor Control CM-813 (continued) • If systems voltage drops below 11.0 vdc the compressor is shut down. Compressor will restart after satisfactory rise in system voltage and rule 3 is satisfied. • The A/C system latches off for any of the following • Low pressure • Open clutch circuit • Shorted clutch circuit

18. Description of Diagnostic Faults • Static Low Pressure • Dynamic Low Pressure • High Pressure • Open Clutch • Shorted Clutch • Low Psw Open • High Psw Open • Low Voltage

19. APADs System Installed on A/C System

20. ACPU Control Module Connectors

21. ACPU Control Functions CM-820 • A/C Start Delay • Compressor Lubrication • Cycle Limiting • TStatSensor • High Pressure Cutout • Low Pressure Cutout • Low Voltage Cutout • High Voltage Cutout • Diagnostic Latch Out

22. Pressure Switches

23. ACPU Control Module

24. Inputs for ACPU CM-820 Controller • LPx- Low pressure switch • HPx- High pressure switch • Tstat- Evaporator Thermostat

25. Outputs for ACPU CM-820 Controller • A/C Drive (Compressor Clutch) • DATA + and DATA – • Fan (Fan Actuator) • Diagnostic Codes

26. Summary • The APAD control system is composed of an electronic control module, two pressure switches, and a conventional evaporator thermostat. • The module receives signals from the two pressure switches and the Tstat, and possibly from the vehicle SAE J1587 data bus. • The inputs are interpreted by control laws, which derive outputs to the compressor clutch, fan actuator circuit, and diagnostic codes.

27. Summary (continued) • In the APADS system, the controller becomes the only device through which power is switched to the compressor clutch coil. • A/C reliability is improved by actively monitoring system conditions and by controlling the compressor and the on-off fan drive. • The CM-813 receives inputs from the following sensors: HPx, LPx, and Tstat.

28. Summary (continued) • The control module delivers outputs to the following locations: A/C drive fan, and diagnostic info to the LEDs or data bus. • APAD and ACPU prevent rapid cycling of the compressor clutch due to high or low pressure conditions. • APAD and ACPU prevent rapid cycling of engine fan at idle. • APAD and ACPU prevent slippage of compressor due to low voltage. • APAD and ACPU relieve stress on the starting system by holding of A/C until 15 seconds after startup.

29. Summary (continued) • APAD and ACPU systems lubricate the A/C compressor and components year round by cycling the compressor for 15 seconds after startup. • APAD and ACPU display fault codes in blink format or as messages on the vehicles dash to indicate potential A/C problems and troubleshooting. • Fault codes may be cleared on some systems by cycling ignition on-off four times or using a data bus tool like Service Pro or Prolink.