Main Power Supply and Ground Circuit Check

Power Supply Circuit Check for Auto A/C System
Check power supply circuit for auto air conditioning system.
Refer to "POWER SUPPLY ROUTING" and Wiring Diagram.

Steps 1 - 2:

A/C System Circuit

SYMPTOM: A/C system does not come on.




CONTROL SYSTEM - ELECTRONIC AUTOMATIC TEMPERATURE CONTROL UNIT (EATC UNIT)
The EATC unit 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, front blower motor and compressor are then controlled.

The EATC unit is unitized with control mechanisms. Signals from various switches are directly entered into EATC unit.
Self-diagnostic functions are also built into EATC unit to provide a quick check of malfunctions in the auto air conditioner system.

Ambient Temperature Input Process
The EATC unit includes a "processing circuit" for the ambient temperature sensor input. When a temperature increase less than 12 °C (20 °F) is detected by the ambient temperature sensor, the "processing circuit" allows the EATC unit to recognize the temperature increase after 80 seconds. When the temperature increase is greater than 12 °C (20 °F) 5 minutes is required.

As an example, consider stopping for a cup of coffee after high speed driving. Even though the actual ambient temperature has not changed, the temperature detected by the ambient sensor will increase because heat radiated from the engine compartment can radiate to the grille area (where the ambient temperature sensor is located).

Sunload Input Process
The EATC unit includes a processing circuit to "average" variations in detected sunload over a period of time. This prevents drastic swings in the EATC 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. The (insignificant) effect of the trees momentarily obstructing the sunlight does not cause any change in the EATC 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.




English/Metric Mode
English or metric can be selected for the display mode.
1. Turn ignition switch ON.
2. Push any mode switch except OFF.
3. Press DEFROST and A/C switches holding the blower switch in the upward position for 1 second.
4. The display mode will be changed to English or Metric.