Air Conditioner Control System
OVERVIEW OF CONTROL SYSTEM
The control system consists of input sensors, switches, the automatic amplifier (microcomputer), and outputs. The relationship of these components is shown in the diagram:
CONTROL SYSTEM INPUT COMPONENTS
Control Unit
By means of multiplex communication, the control unit signals to the auto amp. the switch position and display mode.
Potentio Temperature Control (PTC)
The PTC is built into the auto amplifier. It can be set at intervals of 0.5° C (1.0° F) in the 18° C (65° F) to 32° C (85° F) temperature range by rotating the temperature switch. Setting temperature is digitally displayed.
In-Vehicle Sensor
The in-vehicle sensor is attached to cluster lid C. It converts variations in temperature of compartment air drawn from the aspirator into a resistance value. It is then input into the auto amplifier. (A more detailed description of the aspirator is shown.)
After disconnecting in-vehicle sensor harness connector, measure resistance between terminals (1) and (2) at sensor harness side, using the table.
Aspirator
The aspirator is located below the side link of heater unit. It produces vacuum pressure due to air discharged from the heater unit, continuously taking compartment air in the aspirator.
Ambient Sensor
The ambient sensor is attached in front of the driver's side condenser. It detects ambient temperature and converts it into a resistance value which is then input to the auto amplifier.
After disconnecting ambient sensor harness connector, measure resistance between terminals (1) and (2) at sensor harness side, using the table.
Sunload Sensor
The Sunload sensor is located on the left defroster grille. It detects Sunload entering through windshield by means of a photo diode. Then, it converts the Sunload into a current value which is input to the auto amplifier.
Measure voltage across terminal No. 46 and body ground.
^ When checking sun load sensor, select a place where sun shines directly on it.
^ Sunload under direct sunlight is equivalent to approximately 0.768 kW (660 kcal/h, 2,619 BTU/h)/Sq.m [0.0713 kW (61.31 kcal/h, 243.3 BTU/h)/sq.ft].
Intake Sensor
The intake sensor is located on the cooling unit. It converts temperature of air after it passes through the evaporator into a resistance value. The value is then input to the auto amplifier.
After disconnecting intake sensor harness connector, measure resistance between terminals (2) and (1) at sensor harness side, using the table.
Control System Automatic Amplifier
The auto amplifier has a built-in microcomputer which processes information sent from various sensors needed for air conditioner operation. The air mix door motor, mode door motor, intake door motor, max. cold door motor, blower motor and compressor are then controlled.
The auto amplifier is unitized with control mechanisms. Signals from various switches and Potentio Temperature Control (PTC) are directly entered into auto amplifier.
Self-diagnostic functions are also built into auto amplifier to provide quick check of malfunctions in the auto air conditioner system.
Ambient Temperature Input Process
The automatic amplifier includes a "processing circuit" for the ambient sensor input. When the ambient temperature increases quickly, the processing circuit controls the input from the ambient sensor. It allows the auto amp. to recognize the increase of temperature only 0.33° C (0.6° F) per 100 seconds.
As an example, consider stopping for a cup of coffee after high speed driving. Even though the actual ambient temperature has not changed, the ambient sensor will detect the increase of temperature. The heat radiated from the engine compartment can radiate to the front grille area. The ambient sensor is located there.
Sunload Input Process
The auto amp. also includes a processing circuit which "average" the variations in detected Sunload over a period of time. This prevents drastic swings in the ATC system operation due to small or quick variations in detected Sunload.
For example, consider driving along a road bordered by an occasional group of large trees. The Sunload detected by the Sunload sensor will vary whenever the trees obstruct the sunlight. The processing circuit averages the detected Sunload over a period of time. As a result, the above-mentioned effect does not cause any change in the ATC system operation. On the other hand, shortly after entering a long tunnel, the system will recognize the change in Sunload, and the system will react accordingly.
CONTROL SYSTEM OUTPUT COMPONENTS
Air Mix Door Control (Automatic temperature control)
Component parts
Air mix door control system components are:
1. Auto amplifier
2. Control unit (PTC)
3. Air mix door motor (PBR)
4. In-vehicle sensor
5. Ambient sensor
6. Sunload sensor
7. Intake sensor
System operation
Temperature set by Potentio Temperature Control (PTC) is compensated through setting temperature correction circuit to determine target temperature.
Auto amplifier will operate air mix door motor to set air conditioning system in HOT or COLD position, depending upon relationship between conditions (target temperature, Sunload, in-vehicle temperature and ambient temperature) and conditions (air mix door position and intake air temperature).
When set temperature is 18° C (65° F), air mix door motor will be in the FULL COLD position; when set temperature is 32° C (85° F), motor will be in the FULL HOT position.
Air mix door control specification
Air Mix Door Motor
The air mix door motor is attached to the heater unit. It rotates so that the air mix door is opened to a position set by the auto amplifier. Motor rotation is then conveyed through a shaft. Air mix door position is then fed back to the auto amplifier by PBR built-in air mix door motor.
Air Mix Door Operation
PBR Characteristics
PBR
Measure voltage between terminals (1) and (9) at vehicle harness side.
Ignition Switch: ON
^ Ensure tester pointer deflects smoothly when PTC is moved from 18° C (65° F) to 32° C (85° F) and vice versa.
MAX. Cold Door Control
Component Parts
Max. cold door control system components are:
1. Auto amplifier
2. Max. cold door motor
3. Control unit (PTC)
4. Air mix door motor (PBR)
5. In-vehicle sensor
6. Ambient sensor
7. Sunload sensor
8. Intake sensor
System Operation
The auto amplifier will activate the max. cold door motor and open it when the air outlets are set to the B/L position. It will also activate when the air mix door is set to the "FULL COLD" position with air outlets set to VENT. In all other modes the max. cold door is closed.
MAX. Cold Door Motor
The max. cold door motor is attached to the heater unit. It rotates so that the max. cold door is opened to the position set by the auto amplifier.
Motor rotation is conveyed to a link which activates the max. cold door.
Outlet Door Control
Component Parts
Outlet door control system components are:
1. Auto amplifier
2. Control unit (PTC, and AUTO, ECON, MODE, DEFROSTER switches)
3. Mode door motor
4. PBR
5. In-vehicle sensor
6. Ambient sensor
7. Sunload sensor
8. Intake sensor
System Operation
The auto amplifier computes the air outlet conditions according to the ambient temperature and the in-vehicle temperature. The computed outlet conditions are then corrected for Sunload to determine air outlet. The
determined amount of air is discharged into the passenger compartment.
When the air outlet is automatically selected as FOOT/DEF, the actual outlet will be either F/D1 or F/D2. It will depend on the target temperature and the ambient temperature.
When the OFF switch is pushed, the auto amplifier sets the mode door at the "F/D 1" position.
Outlet Door Control Specification
FOOT/DEF Mode Specification
^ When The air outlet is automatically selected as F/D, when target temperature is high, the air outlet is fixed at F/D 1.
^ When the target temperature is low, the air outlet will be either F/D 1 or F/D 2 depending on the ambient temperature.
^ When the ambient temperature decreases to -13° C (9° F), air outlet is changed from F/D 1 to F/D 2.
^ When the ambient temperature increases to -8° C (18° F), air outlet is changed from F/D 2 to F/D 1.
Mode Door Motor
The mode door motor is attached to the heater unit. It rotates so that air is discharged from outlet set by the auto amplifier. Motor rotation is conveyed to a link which activates the mode door.
Mode Door Motor Operation
Intake Door Control
Components Parts
Intake door control system components are:
1. Auto amplifier
2. Control unit
(PTC, AUTO, ECON, DEFROSTER, RECIRCULATION switches)
3. Intake door motor
4. PBR
5. In-vehicle sensor
6. Ambient sensor
7. Sunload sensor
8. Intake sensor
System Operation
The intake door control determines the intake door position based on both ambient and in-vehicle temperature. When the ECON, DEFROSTER, or OFFswitches are pushed, the auto amplifier sets the intake door at the "Fresh" position. When the compressor is turned OFF from ON (to prevent the auto amplifier from becoming frozen), the intake door is automatically changed to the "Fresh" position (even if it has been set at the "RECIRCULATION" position).
Intake Door Control Specification
Intake Door Motor
The intake door motor is attached to the intake unit. It rotates so that air is drawn from inlets set by the auto amplifier. Motor rotation is conveyed to a lever which activates the intake door.
Intake Door Motor Operation
Fan Speed Control
Component Parts
Fan speed control system components are:
1. Auto amplifier
2. Control unit
(PTC, AUTO, ECON, MODE, DEFROSTER, BLOWER, OFF switches)
3. Fan control amplifier
4. PBR
5. In-vehicle sensor
6. Ambient sensor
7. Sunload sensor
8. Intake sensor
9. Hi relay
10. Thermal transmitter
SYSTEM DESCRIPTION
Automatic Mode
In the automatic mode, the blower motor speed is calculated by the automatic amplifier based on inputs from the PBR, in-vehicle sensor, Sunload sensor, and ambient sensor. The blower motor applied voltage ranges from approximately 5 Volts (lowest speed) to 12 Volts (highest speed).
The control blower speed (in the range of 5 to 10.5 V), the automatic amplifier supplies a signal to the fan control amplifier. Based on this signal, the fan control amplifier controls the current flow from the blower motor to ground. If the computed blower voltage (from automatic amplifier) is above 10.5 Volts, the high blower relay is activated. The high blower relay provides a direct path to ground (bypassing the fan control amplifier), and the blower motor operates at high speed.
Starting Blower Speed Control
Start up from "COLD SOAK" condition (Automatic mode)
In a cold start-up in the following conditions the blower will not operate for a short period of time (up to 150 seconds): 1) Engine temperature is below 50° C (122° F), 2) Air outlet has been automatically set to B/L or FOOT/DEF. The exact start delay time varies depending on the outlet door control and engine temperature. In the most extreme case (very low ambient) the blower starting delay will be 150 seconds as described above. After this delay, the blower will operate at low speed until the engine temperature rises above 50° C (122° F). From this point the blower speed will increase to the target speed.
Start up from normal or "HOT SOAK" condition
(Automatic mode)
The blower will begin operation momentarily after the AUTO button is pushed. The blower speed will gradually rise to the objective speed over a time period of 5 seconds or less (actual time depends on the objective blower speed).
The blower will stop for 3 seconds after it has started with the compressor coming ON at a recirculating air temperature greater than 35° C (95° F).
Blower Speed Compensation
Sun load
When the in-vehicle temperature and the set temperature are very close, the blower will be operating at low speed. The low speed will vary depending on the Sunload. During conditions of high Sunload, the blower low speed is "normal" low speed (approx. 6 V). During low or no Sunload conditions, the low speed will drop to "low" low speed (approx. 5 V).
Ambient
When the ambient temperature is in the "moderate" range [10 - 15° C (50 - 59° F)], the computed blower voltage will be compensated (reduced) by up to 3.5 V (depending on the blower speed). In the "extreme" ambient ranges [below 0° C (32° F) and above 20° C (68° F)] the computed objective blower voltage is not compensated at all. In the ambient temperature ranges between "moderate" and "extreme" [0 - 10° C (32 - 50° F) and 15 - 20° C (59 - 68° F)], the amount of compensation (for a given blower speed) varies depending on the ambient temperature.
On-Coming Air
With intake position at "FRESH" while driving at speeds exceeding 80 kph (50 MPH), blower motor voltage will lower to a minimum 1.5 Volts. This is to prevent an abrupt increase in airflow due to ram pressure.
Mode
If the mode door motor starts up when the blower motor voltage exceeds 8.5 Volts, the auto amplifier will lower the voltage to 8.5 Volts.
Fan speed control specification
Fan Control Amplifier
The fan control amplifier is installed on the intake unit. It amplifies the base current of the auto amplifier and controls the blower fan motor speed.
HI Relay
The Hi relay is located on the intake unit. It receives a signal from the auto amplifier to operate the blower motor at high speed.
Magnet Clutch Control
Auto amplifier controls compressor operation by ambient temperature, intake temperature, and signal from ECCS control module.
Low temperature protection control
Auto amplifier will turn the compressor "ON" or "OFF" as determined by a signal detected by ambient temperature sensor and intake sensor.
When ambient temperatures are greater than 12° C (54° F), the compressor turns "ON". The compressor turns "OFF" when ambient temperatures are less than -7° C (19° F).
Between the ambient temperatures 12° C (54° F) and -7° C (19° F), the auto amplifier controls the compressor ON - OFF operation as determined by a signal from the intake sensor.
Acceleration cut control
The ECCS control module will turn the compressor "ON" or "OFF" based on the signal from the throttle sensor and vehicle speed sensor.