Copyright © 2014 Delmar, Cengage Learning APAD/ACPU A/C Control Systems Instructor Name: (Your Name) 11 CHAPTER

Copyright © 2014 Delmar, Cengage Learning

APAD/ACPU A/C Control Systems

Instructor Name: (Your Name)

11CHAPTER


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.


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.


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.


Volvo APADs Unit Mounted on Truck’s Firewall


Electronically Managed HVAC Systems

APAD- Air Conditioning Protection and Diagnostics.

ACPU- Air Conditioning Protection Unit.


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.


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.


Functions of APAD (continued)

Helps reduce A/C operating costs by:1. Prevent rapid compressor cycling.

2. Prevent rapid cycling of engine fan at idle.

3. Prevent compressor clutch slippage due to low voltage.

4. Relieve stress on starting system by holding off A/C until 15 seconds after startup.

5. Lubricate system by cycling compressor for 15 seconds after start up.

6. Show system fault codes.


Inputs and Outputs, Line diagram


Inputs for ACPU-813 Controller

HPx- High pressure switch LPx- Low pressure switch TStat- Evaporator thermostat switch


Pressure Switch


Pressure Switch on Vehicle


Outputs for ACPU CM813 Controller

A/C Drive (compressor clutch drive) Fan (Engine fan actuator) Diagnostic LEDs


APADS Rules for Compressor Control (CM-813)

1. Compressor never turns on until 15 seconds after ignition switch is turned on.

2. 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.

3. The compressor cycle rate is limited to one time every 15 seconds.

4. The Tstat is the primary controller.


APADS Rules for Compressor Control CM-813 (continued)

5. 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.

6. In a low pressure condition the compressor is shut down. Compressor will restart after LPx resets and rules 3 and 8 are satisfied.


APADS Rules for Compressor Control CM-813 (continued)

7. 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.

8. The A/C system latches off for any of the following Low pressure Open clutch circuit Shorted clutch circuit


Description of Diagnostic Faults

Static Low Pressure Dynamic Low Pressure High Pressure Open Clutch Shorted Clutch Low Psw Open High Psw Open Low Voltage


APADs System Installed on A/C System


ACPU Control Module Connectors


ACPU Control Functions CM-820

A/C Start Delay Compressor Lubrication Cycle Limiting TStat Sensor High Pressure Cutout Low Pressure Cutout Low Voltage Cutout High Voltage Cutout Diagnostic Latch Out


Pressure Switches


ACPU Control Module


Inputs for ACPU CM-820 Controller

LPx- Low pressure switch HPx- High pressure switch Tstat- Evaporator Thermostat


Outputs for ACPU CM-820 Controller

A/C Drive (Compressor Clutch) DATA + and DATA – Fan (Fan Actuator) Diagnostic Codes


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.


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.


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.


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.

Documents

Copyright © 2014 Delmar, Cengage Learning APAD/ACPU A/C Control Systems Instructor Name: (Your Name) 11 CHAPTER