Transcript APAD/ACPU A/C Control Systems

CHAPTER
11
APAD/ACPU A/C
Control Systems
Instructor Name: (Your Name)
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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.
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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.
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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.
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Volvo APADs Unit Mounted on
Truck’s Firewall
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Electronically Managed HVAC
Systems
 APAD- Air Conditioning Protection
and Diagnostics.
 ACPU- Air Conditioning Protection
Unit.
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Advantages of APAD
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Actively monitoring system conditions.
Controls the A/C compressor.
Controls the engine cooling fan.
Does not allow operation in unstable or selfdestructive modes.
 Provides diagnostic codes to technician for
service and troubleshooting.
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Functions of APAD
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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.
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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.
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Inputs and Outputs, Line diagram
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Inputs for ACPU-813 Controller
 HPx- High pressure switch
 LPx- Low pressure switch
 TStat- Evaporator thermostat switch
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Pressure Switch
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Pressure Switch on Vehicle
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Outputs for ACPU CM813 Controller
 A/C Drive (compressor clutch drive)
 Fan (Engine fan actuator)
 Diagnostic LEDs
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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.
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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.
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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
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Description of Diagnostic Faults
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Static Low Pressure
Dynamic Low Pressure
High Pressure
Open Clutch
Shorted Clutch
Low Psw Open
High Psw Open
Low Voltage
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APADs System Installed on A/C
System
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ACPU Control Module Connectors
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ACPU Control Functions CM-820
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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
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Pressure Switches
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ACPU Control Module
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Inputs for ACPU CM-820 Controller
 LPx- Low pressure switch
 HPx- High pressure switch
 Tstat- Evaporator Thermostat
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Outputs for ACPU CM-820 Controller
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A/C Drive (Compressor Clutch)
DATA + and DATA –
Fan (Fan Actuator)
Diagnostic Codes
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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.
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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.
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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.
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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.
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