System Description

The Automatic Temperature Control (ATC) system provides automatic regulation of the vehicles interior temperature. The operator selects "set temperature", on which the regulation is based, regardless of the outside temperature changes. This is done by utilizing a microcomputer, also referred to as the automatic amplifier, which receives input signals from several sensors. The automatic amplifier (BCM) uses these input signals (including the set temperature) to automatically control the ATC system's outlet air volume, air temperature, and air distribution.

Features
Air mix door control (Automatic temperature control)
The air mix door is automatically controlled so that in-vehicle temperature is maintained at a predetermined value by: The temperature setting, ambient temperature, in-vehicle temperature and amount of sunload.

Fan speed control
Blower speed is automatically controlled based on temperature setting, ambient temperature, in-vehicle temperature, amount of sun load and air mix door position.
With FAN switch set to "AUTO", the blower motor starts to gradually increase air flow volume.
When engine coolant temperature is low, the blower motor operation is delayed to prevent cool air from flowing.

Intake door control
The intake doors are automatically controlled by: The temperature setting, ambient temperature, in-vehicle temperature, amount of sun load and ON-OFF operation of the compressor.

Outlet door control
The outlet door is automatically controlled by: The temperature setting, ambient temperature, in-vehicle temperature and amount of sunload.

Magnet clutch control
The ECM (ECCS control module) controls compressor operation using input signals from the throttle position sensor and auto amplifier.

Self-diagnostic system
The self-diagnostic system is built into the auto amplifier (BCM) to quickly locate the cause of problems.





Overview of Control System
The control system consists of a) input sensors and switches, b) the auto amp. (microcomputer), and c) outputs. The relationship of these components is shown in the diagram above:

Air Mix Door Control (Automatic Temp. Control)



Component parts
Air mix door control system components are:
1. Auto amp.
2. Air mix door motor (PBR)
3. In-vehicle sensor
4. Ambient sensor
5. Sunload sensor

System operation
Temperature set by Potentio Temperature Control (PTC) is compensated through setting temperature correction circuit to determine target temperature. Auto amp. 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 compressor operation).




Air Mix Door Control Specification




Air Mix Door Motor
The air mix door motor is attached to the bottom of the heater unit. it rotates so that the air mix door is opened to a position set by the auto amp. Motor rotation is then conveyed through a shaft and air mix door position is then fed back to the auto amp. by PBR built-in air mix door motor.







Air Mix Door Motor Operation





PBR Characteristics
Measure resistance between terminals 1 and 2 at vehicle harness side.


Mode Door Control



Component parts
Mode door control system components are:
1. Automatic Amplifier.
2. Mode door motor
3. PBR
4. In-vehicle sensor
5. Ambient sensor
6. Sunload sensor

System operation
The Automatic Amplifier computes the air discharge conditions according to the ambient temperature and the in-vehicle temperature. The computed discharge conditions are then corrected for Sunload. By this correction, it is determined through which outlets air will flow into the passenger compartment.




Mode Door Control Specification










Mode Door Motor
The mode door motor is attached to the heater unit. It rotates so that air is discharged from the outlet set by the automatic amplifier. Motor rotation is conveyed to a link which activates the mode door.





Intake Door Control
Components parts
Intake door control system components are:
1. Auto amp.
2. Intake door motor
3. PBR
4. In-vehicle sensor
5. Ambient sensor
6. Sunload sensor

System operation
The intake door control determines intake door position based on the ambient temperature and the in-vehicle temperature. When the ECON, DEF, or OFF buttons are pushed, the auto amp. sets the intake door at the "Fresh" 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 amp. 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 amp.
2. Fan control amplifier
3. PBR
4. In-vehicle sensor
5. Ambient sensor
6. Sun load sensor
7. Thermal transmitter




Fan Speed Control Specification





Fan Control Amplifier
The fan control amplifier is located on the cooling unit. It amplifies the base current flowing from the auto amp. to change the blower speed within the range of 4V to 12V.

AUTOMATIC MODE
In the automatic mode, the blower motor speed is calculated by the auto amp. based on inputs from the PBR, in-vehicle sensor, Sunload sensor, and ambient sensor. The blower motor applied voltage ranges from approximately 4.5 Volts (lowest speed) to 12 Volts (highest speed).
To control blower speed, the auto amp. supplies a signal (in the range to 2.5V to 9V), to the fan control amplifier. Based on this signal, the tan control amplifier controls the current flow from the blower motor to ground.

STARTING FAN SPEED CONTROL
Start up from "COLD SOAK" condition (Automatic mode)
In a cold start up condition where the engine coolant temperature is below 50° C (122°F), the blower will not operate for a short period of time (up to 150 seconds). The exact start delay time varies depending on the ambient and engine coolant temperature. In the most extreme case (very low ambient) the blower starting delay will be 150 seconds. After this delay, the blower will operate at low speed until the engine coolant temperature rises above 50° C (122° F). Then the blower speed will increase to the objective 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).

BLOWER SPEED COMPENSATION
Sun load
When the in-vehicle temperature and the set temperature are very close, the blower will operate at low speed. The low speed varies depending on the Sunload. During conditions of high Sunload, the blower low speed is "normal" low speed (approx. 5.5V). During lesser Sunload conditions, the low speed will drop to "low" low speed (approx. 4.5V).

Magnet Clutch Control
The Engine Control Module ECM (ECCS control module) controls compressor operation using inputs from the throttle position sensor and auto amplifier.




Low Temperature Protection Control
Auto amplifier will turn the compressor "ON" or "OFF" as determined by a signal detected by ambient temperature sensor. The compressor turns "OFF" when ambient temperatures are less than -1° C (30° F).

Acceleration cut Control
The Engine Control Module (ECM) (ECCS control module) will turn the compressor "ON" or "OFF" based on the signal from the throttle position sensor.