Chapter 21 Chassis System Electronics 411
Copyright by Goodheart-Willcox Co., Inc.
specifi c designs vary, you should understand the construction
and operation of typical components. The basic parts of an
electronic climate control system include:
Control panel—dash panel containing switches for
programming the processor.
Power supply—electronic circuit that provides con-
stant DC voltage to an ECM, and sometimes to a dis-
play or other components.
Vacuum actuator—actuator that uses ECM signals to
control vacuum supply to various vacuum diaphragms.
Control module—small electronic circuit that is some-
times used to control a blower motor and air condi-
tioning compressor clutch.
Vacuum diaphragms—flexible vacuum-operated cham-
bers that serve as output devices for moving airfl ow
control doors.
A complete circuit for a modern climate control system
is shown in Figure 21-27. Note how the climate control
ECM receives signals from numerous sensors: outside air
temperature, evaporator temperature, heater core tempera-
ture, sunlight, humidity, AC pressure, engine coolant, and
in-car temperature sensors. The climate control ECM can
then electrically energize the AC compressor clutch, air
mix control doors under the dash, blower or recirculation
blower or fan, mode control motor, and other devices in
the system.
Electronic Cruise Control System
A modern electronic cruise control system uses an
ECM, sensors, and a throttle actuator to maintain vehicle
speed when highway driving. The major parts of a typical
system are in Figure 21-28. These parts include:
Power switch—feeds current to the ECM to activate
and ready the system for operation.
Control switch—signals the ECM to maintain present
vehicle speed when activated.
Vehicle speed sensor—feeds pulsing signal that repre-
sents velocity of the car in mph or kmh into the ECM.
Cruise ECM—uses input signals to control outputs to a
throttle actuator.
Throttle actuator—physically moves the engine throt-
tle lever to control engine power and resulting vehicle
speed.
Brake light switch—stoplight switch that signals the ECM
to shut off the cruise control when the brakes are applied.
Clutch switch—signals the ECM to deactivate the
cruise control when the clutch pedal is depressed.
Neutral safety switch—signals the ECM to shut off the
cruise when the shift lever is moved out of drive to
prevent engine racing.
Power
Supply
Microprocessor
Battery
Vacuum
Actuator
Ambient Temperature Sensor
In-Car Temperature Sensor
Vacuum Source
A/C Compressor
Clutch
Control
Module
Solenoids
Air Inlet
Door
Blower
A/C
Core
Heater
Core
Temperature
Door
Lower
Mode
Door
Upper
Mode
Door
Vacuum Diaphrams
Electronic Touch Climate Control
Membrane Switch
Control Panel
Vacuum
Fluorescent
Temperature
Display
Rear Defog Display
Ignition
Figure 21-26. Diagram shows a typical electronic climate control system. Study the part relationships.