Self-diagnosis of the Toyota Camry air conditioner control unit

The air conditioning control unit has a self-diagnosis function

Information about malfunctions in the air conditioning system is stored in the system memory in the form of fault codes

Using the buttons on the remote control of the air conditioner, you can display the fault codes stored in the memory.

Since the system memory that stores the fault codes is powered by the battery, the fault codes are stored even when the ignition is turned off.

Fig. 1. Self-diagnosis function start-up diagram

Control - Description

Air temperature control

In response to setting the temperature selection switch, the desired outlet air temperature is corrected to the desired temperature by the evaporator temperature sensor and the coolant temperature sensor, used by the air mixture damper control to calculate the preliminary opening angle.

With the help of an arithmetic chain of calculations of the electronic control unit, the required opening angle of the damper is achieved

Fan control

This function controls the operation of the fan motor according to the signals from the coolant temperature sensor, evaporator temperature sensor and solar sensor.

In addition, the fan motor controller is protected against a sudden surge of current that occurs when the fan motor is started

Air distribution control

When the AUTO switch is in the ON position, automatic control acts on the servomotor (air mixture control) to open the damper to the target angle, the value of which is based on the calculation of the desired outlet air temperature.

In addition, in automatic control, the servomotor potentiometer (air mixture control) is used to detect the actual damper opening angle and adjust it according to the target damper opening angle

According to the coolant temperature, outdoor air temperature, amount of sunlight, desired fan outlet temperature and vehicle driving conditions, this control will automatically switch the blower mode to FOOT/DEF to prevent fogging of the windows at low outdoor temperatures</ p>

Air intake control

Operates the (air inlet) servomotor according to the position of the air inlet control switch and sets the dampers to RECIRC (recirculation) or FRESH (fresh air) position

When the compressor is turned off manually or by automatic control, the air conditioning control unit switches the air intake mode to FRESH (fresh air).

When the outdoor temperature is low, the air conditioning control unit automatically switches the air intake mode to FRESH (fresh air) to prevent fogging of the windows

Compressor control

This control disables the compressor magnetic clutch when the fan motor is off, when the coolant temperature is below a certain value, the refrigerant pressure signal is incorrect, or the evaporator discharge temperature is insufficient

When the DEF mode switch is in the ON position, the magnetic clutch relay turns on automatically to start the compressor.

Also, when the fan is off and the front heating vent switch is in the ON position, the fan will turn on automatically

Rear window heating control

When the heated rear window is turned on, the rear window and door mirror heaters will operate.

The heating will automatically turn off after 15 minutes


Checks if the sensor signals correspond to the operation mode set by the switches on the air conditioner panel, in this case, the control panel displays a diagnostic code (malfunction code) indicating the presence or absence of a malfunction (sensor test function)

Toyota Camry air conditioner control unit functions

In sequence, actuates the actuators according to the position of the air conditioner switches (actuator test function)