1.Air mix servomotor
(1)Construction
The air mix servomotor consists of the motor, limiter, potentiometer and moving contact, etc., as shown in the figure and it is activated by the signal from the ECU.
(2)Operation
When the air mix damper is shifted to HOT, the MH terminal will be the power source and the MC terminal will be the ground to rotate the servomotor to make the shift. When the MC terminal becomes the power source and the MH terminal becomes the ground, the servomotor rotates in the opposite direction to shift the air mix damper to COOL.
The moving contact of the potentiometer moves in synchronicity with the servomotor revolving, generates electric signals according to the damper position, and feeds back the actual damper position to the ECU. When the damper comes to the desired position, the air mix servomotor stops the current to the servomotor.
The air mix servomotor is equipped with a limiter that shuts off the current to the motor when full-stroke movement is activated. When the moving contact that synchronizes with the servomotor revolving reaches the full-stroke positions, the circuit is open to stop the motor.
2.Air inlet servomotor
(1)Construction
The air inlet servomotor consists of the motor, gear, moving plate, etc., as shown in the figure.
(2)Operation
Pressing the air inlet control switch will generate the ground circuit for the servomotor to allow the current to the motor and moves the air inlet damper.
When the damper is changed to FRESH or RECIRC position, the contact of the moving plate linked with the motor is released and the circuit is open to stop the motor.
3.Airflow servomotor
(1)Construction
The airflow servomotor consists of the motor, moving contact, circuit plate, motor drive circuit, etc., as shown in the figure.
(2)Operation
When the airflow control switch is operated, the motor drive circuit determines whether the damper position changes to the right or left side and directs the flow of current to the motor to shift the moving contact linked to the motor.
When the moving contact moves to the position according to the airflow control switch position, the contact with the circuit plate is released, the circuit is open and the motor stops.
When the airflow control switch is moved from FACE to DEF
Input A will be 1 because the circuit is open, and input B will be 0 because the grounded circuit is generated. As a result, output D will be 1 and output C will be 0 and allow the current for the motor from D to C. After the motor revolves and moving contact B releases contact with DEF, input B will be 1 because the circuit will be opened. As a result, both output C and D will be 0, the current to the motor is cut and the motor stops.
Some models do not have a contact in the servomotor.
A/C control ECU rotates the motor based on the operation of the selector on the control panel.
Damper position is monitored in reference to the potentiometer voltage that varies according to the motor.

1.Interior temperature sensor
(1)Construction
The interior temperature sensor uses the thermistor and is installed in the instrument panel with the aspirator. The aspirator utilizes the air blown from the blower to suck the air inside the vehicle in order to detect the average interior temperature.
(2)Function
It detects the interior temperature that is used as the basis for the temperature control.
2.Ambient temperature sensor
(1)Construction
The ambient temperature sensor uses the thermistor and is installed at the front of the condenser. It detects the exterior temperature.
(2)Function
It detects the exterior temperature that is used for controlling the fluctuation of the interior temperature caused by the exterior temperature fluctuation.
3.Solar sensor
(1)Construction
The solar sensor uses a photodiode and is installed in the upper portion of the instrument panel. It detects the amount of sunlight.
(2)Function
It detects the amount of sunlight that is used for controlling the fluctuation of the interior temperature caused by the amount of sunlight fluctuation.
4.Evaporator temperature sensor
(1)Construction
The evaporator temperature sensor uses the thermistor and is installed on the evaporator. It detects the temperature of the air passing through the evaporator (surface temperature of the evaporator).
(2)Function
It is used for frost prevention, temperature and time-lag airflow control.
5.Water temperature sensor
(1)Construction
The water temperature sensor uses the thermistor. It detects the coolant temperature based on the engine water temperature sensor. The signal is transmitted from the engine ECU.
In some models, the water temperature sensor is installed at the heater core.
(2)Function
It is used for temperature control, warm-up control, etc.
Some vehicles are equipped with the following sensors.
Duct sensors
The duct sensors use the thermistor and are installed at inside of the side register. It detects the temperature of the air blown toward the side register and precisely controls the air temperature of the individual airflow.
Smog ventilation sensor
The smog ventilation sensor is installed in the front portion of the vehicle and detects the level of CO (carbon monoxide), HC (hydrocarbons), and NOx (oxides of nitrogen) to control switching between FRESH and RECIRC.

Outline

1.    Auto A/C (Air Conditioner) System
The auto A/C system is activated by setting the desired temperature with the temperature selector and pressing the AUTO switch. The system immediately adjusts and maintains the temperature at the set level with the automatic control of the ECU.

Location
The auto A/C is controlled by the following components:
1.A/C control ECU (or A/C amplifier)
2.Engine ECU
3.Control panel
4.Interior temperature sensor
5.Ambient temperature sensor
6.Solar sensor
7.Evaporator temperature sensor
8.Water temperature sensor (engine ECU sends the signal)
9.A/C pressure switch
10.Air mix servomotor
11.Air inlet servomotor
12.Airflow servomotor
13.Blower motor
14.Blower controller (controls blower motor)
In some models, the following components are also used for the auto A/C control.
Duct sensors
Smog ventilation sensor

ECU

1.A/C control ECU
The ECU computes the temperature and volume of the air to be blown and determines which vents to use based on the temperature detected by each sensor and the set temperature.
These values are used to control the air mix damper position, blower motor speed, and airflow damper positions.
In some models, MPX (multiplex communication system) is used to transmit operation signals from the control panel to the A/C control ECU.

1.Description
For cooling performance of the A/C, measure the difference of temperature between the inlet port and outlet port of the air, and judge whether the value is within the standard range in the standard performance chart.
2.Test condition
Test the vehicle in the following conditions:
Stopping condition in shade
Engine coolant temperature: After warm-up
All doors: Fully open
Airflow selector: “FACE”
Air inlet selector: “RECIRC”
Engine speed: 1,500 rpm (R-134a), 2,000 rpm (R-12)
Blower speed: HI
Temperature selector: MAX.COOL
A/C Switch: ON
Pressure on the high-pressure side: 1.5MPa (15.5 kgf/cm²)
3.Measure each temperature
Place a dry and wet bulb thermometer at the air inlet and a dry bulb thermometer at the center of the outlet port. When the air temperature at the outlet stabilizes (after approximately 5 to 6 minutes), measure the difference between both dry bulb thermometers and the relative humidity of the air at the air inlet port.
4.How to obtain relative humidity
Apply the temperature of the dry bulb thermometer and of the wet bulb thermometer at the inlet to the psychrometric chart to obtain the relative humidity. For example, when the dry-bulb thermometer is 25°C (77°F) and the wet-bulb thermometer is 19.5°C (67.1°F), the point at which the lines cross is the relative humidity. In this case, it is 60%.
5.How to read performance chart
If the intersection point made by the crossing of both values is within the shaded area, this cooling ability can be judged good.

1.Normal
If the refrigeration cycle is normal, the gauge pressure values are as shown.
Low-pressure side
0.15 to 0.25 MPa (1.5 to 2.5 kgf/cm²)
High-pressure side
1.37 to 1.57 MPa (14 to 16 kgf/cm²)
2.Insufficient refrigerant amount
3.Excessive refrigerant or insufficient condenser cooling
If there is excessive refrigerant or the condenser cooling is insufficient, the gauge pressure for the both the low-pressure and high-pressure side shows as being higher than the normal value.
(1)Symptom
Pressure is high at both low-pressure and high-pressure side.
Bubbles not observed in the sight-glass, even at low speed operation.
Insufficient cooling.
(2)Cause
Excessive refrigerant.
Poor condenser cooling.
(3)Remedy
Adjust to correct refrigerant amount.
Clean the condenser.
Inspect the vehicle cooling system (electric fan, etc.).
4.Moisture in refrigeration cycle
5.Compression defect in compressor
When a compression defect occurs in the compressor, the gauge pressure at the low-pressure side is higher than the normal value. The gauge pressure at the high-pressure side is lower than the normal value.
(1)Symptom
Low-pressure side is high, high-pressure side is low.
Turning off the air conditioner immediately restores the high-pressure side and low-pressure side to the same pressure.
Compressor unit is not hot to the touch.
Insufficient cooling.
(2)Cause
Compressor defect.
(3)Remedy
Inspect and repair the compressor.
Clog in refrigeration cycle

7.Air in refrigeration cycle
When air infiltrates the refrigeration cycle, the gauge pressure at both the low-pressure and high-pressure side is higher than the normal value.
(1)Symptom
Pressure is high at both low-pressure and high-pressure side.
Cooling performance decreases in proportion to the increase in the low-pressure.
If the refrigerant amount is correct, the flow of bubbles at the sight-glass is the same as during normal operation.
(2)Cause
Air infiltration.
(3)Remedy
Replace the refrigerant.
Implement thorough evacuation of the cycle.
8.Excess opening of expansion valve

1.Importance of checking pressure
Checking the refrigerant pressure while the air conditioning is functioning allows you to assume the trouble area or the cause. Therefore, it is important to confirm the appropriate value and to diagnose the trouble.
2.Trouble seeking by using manifold gauge
When performing the trouble diagnosis by using a manifold gauge, follow the conditions below.
Engine coolant temperature: After warm-up
All doors: Fully opened
Airflow selector: “FACE”
Air inlet selector: “RECIRC”
Engine speed: 1,500 rpm (R-134a), 2,000 rpm (R-12)
Blower speed selector: HI
Temperature selector: MAX. COOL
A/C switch: ON
A/C inlet temperature: 30 to 35°C (86 to 95°F)
NOTICE:
For the vehicle with EPR, since the low-pressure side is controlled with EPR, abnormal values may not be indicated directly on the gauge pressure.

1.Is the drive belt loose?
If the drive belt is too loose, it will slip; this will cause it to wear out.
2.Amount of air blow is insufficient
Check for dirt and clog in the clean air filter.
3.Noise heard near compressor
Check the compressor mounting bolts and the bracket mounting bolts.
4.Noise heard inside compressor
Noise could be caused by damaged internal components.
5.Condenser fins covered with dirt and dust
If the condenser fins are covered with dirt and dust, the condenser’s cooling efficiency will be greatly reduced. Wash off all dirt and dust from the condenser.
6.Oil stains on refrigeration system connections or joints
An oil stain on a connection or joint indicates that refrigerant is leaking from that place. If such an oil stain is found, parts should be retightened or replaced as necessary to stop the gas leakage.
7.Noise heard near blower
Turn the blower motor to LO, MED, and HI. If abnormal noise is produced or motor rotation is improper, replace the blower motor.
A foreign object lodged in the blower could also produce noise, and improper mounting of the motor could cause improper rotation, so these points should be fully checked before replacing the blower motor.
8.Checking refrigerant quantity through sight-glass
If a large flow of bubbles can be seen in the sight-glass, there is insufficient refrigerant, so replenish the refrigerant to the proper level. Also check for oil stains at this time, as described above, to make sure that there is no refrigerant leakage. If bubbles cannot be seen in the sight-glass, even when the condenser is cooled by pouring water on it, there is excessive refrigerant in the system, so discharge the refrigerant until the proper quantity remains.
When the system uses a sub-cool type condenser, refrigerant may not be sufficient even if the bubbles cannot be seen.

Notes for Maintenance of Air Conditioning System

1.When handling refrigerant the following precautions must be observed
Do not handle refrigerant in an enclosed area or near an open flame.
Always wear eye protection.
Be careful that liquid refrigerant does not get in your eyes or on your skin.
(1)If liquid refrigerant gets in your eyes or your skin:
Do not rub.
Wash the area with a lot of cool water.
Apply clean petroleum jelly to the skin.
Go immediately to a physician or hospital for professional treatment.
Do not attempt to treat yourself.
2.When replacing parts on refrigerant line
Recover the refrigerant into the refrigerant recovery machine for reuse.
Insert a plug immediately in disconnected parts to prevent entry of moisture and dust.
Do not leave a new condenser or receiver/dryer, etc, lying around with the plug removed.
Discharge nitrogen gas from the charging valve before removing the plug from the new compressor. If the nitrogen gas is not discharged first, compressor oil will spray out with the nitrogen gas when the plug is removed.
Do not use a burner for bending or lengthening tubes.    
3.When tightening connecting parts
Apply a few drops of compressor oil to O-ring fittings for easy tightening and to prevent leakage of refrigerant gas.
Tighten the nut using two opened wrenches to avoid twisting the tube.
Tighten the O-ring fittings or the bolted type fittings to the specified torque.
4.When handling refrigerant container
The container must never be heated.
Containers must be kept below 40°C (104°F).
When warming the container with warm water, be careful that the valve on top of the container is never immersed in the water, as the water may permeate into the refrigeration circuit.
Empty containers must never be re-used.
5.When A/C is on and refrigerant gas is being replenished
If there is not enough refrigerant gas in the refrigeration circuit, oil lubrication becomes insufficient and compressor burnout may occur, so take care to avoid this.
If the valve on the high-pressure side is opened, refrigerant flows in reverse and causes the service can to rupture, so only open and close the valve on the low-pressure side.
If the refrigerant container is inverted and refrigerant is charged in a liquid state, the liquid will be compressed and the compressor will break down, so the refrigerant must be charged in a gaseous state.
Be careful not to charge too much refrigerant gas, as this causes trouble such as inadequate cooling, poor fuel economy, engine overheating, etc.
6.When using halide torch leak detector
Since an open flame is used, there is a danger of igniting explosive gas. The surrounding area should first be checked for the presence of inflammable or explosive materials before using this detector.
Although the R-12 refrigerant is nontoxic, it becomes toxic once it is exposed to an open flame. For this reason, if the color of the flame in the detector changes, be particularly careful not to inhale the gas emitted by the detector.

1.Function
In idle state such as in slow traffic or during stop, the engine output is small.
In this state, driving the compressor applies overload to the engine, which results in overheating or engine stalling. So, an idle-up device is installed to make the idle speed a little higher to use the A/C.
2.Operation
An engine ECU that receives an A/C switch-on signal opens the idle speed control valve a little to increase intake air to make the engine revolve at the appropriate speed.

Electric Fan Control

1.Function
An electric fan cools the condenser when the A/C is in operation to increase the cooling capability.
2.Operation
In the vehicle that cools the radiator by electric fan, combining two fans for radiator and for condenser controls the cooling capability in three levels (stop, low speed, high speed). When the A/C is in operation, the connection of the two electric fans switches to series connection (low speed) or to parallel connection (high speed) depending on the condition of the refrigerant pressure and the coolant temperature.
When refrigerant pressure is high or engine coolant temperature is high, two electric fans are connected in parallel and rotate at a high speed.
When refrigerant pressure is low or engine coolant temperature is low, two electric fans are connected in series and rotate at a low speed.
Recent models have not only the type that switches fan connection by relay (series connection, parallel connection) but also the type that adjusts the current flow into the electric fan by engine ECU and cooling fan ECU.
The connecting method between the relay and fan and ON/OFF operation of the relay vary depending on the model.

1.Function
The dual A/C and the refrigeration cycle with rear cooler have evaporators and expansion valves for front and rear. These make the refrigerant circulate using a compressor.
To control two refrigerant circuits, solenoid valves are set up.
2.Operation
When the front A/C switch is turned on, current passes through the front solenoid valve and it turns on (opens), while current does not pass through the rear solenoid valve, so the valve turns off (closes). Therefore, the refrigerant flows only in the front side circuit.
When the rear A/C switch is turned on, current passes through both the front side and the rear side and both of the valves turn on (open), so refrigerant passes into the refrigerant circuits on the front side and rear side.
In some models, current passes through only the rear solenoid valve when only the rear A/C switch is turned on.