1 air conditioning control circuit composition

The air-conditioning circuit has different control modes due to different models of the model, but no matter which model of the manufacturer, it is mainly composed of the compressor control circuit, the blower control circuit, the condenser fan control circuit, the damper motor control circuit, the sensor circuit, A panel control circuit or the like is formed.

2 air conditioning control circuit analysis

2.1 compressor control circuit

This control circuit is the core of the air conditioning system control. Whether manual air conditioner or automatic air conditioner is deployed around this circuit, other circuits are related to this circuit. The working conditions are AC switch, blower switch, constant temperature switch, pressure switch, refrigerant temperature. The pressure switch must be closed and the engine speed signal and compressor speed signal are normal. When these conditions are met, the compressor will work.

The manual air conditioning circuit generally connects the compressor power circuit in series among several switches. When the integrated amplifier is used, each working condition signal is first input to the amplifier. When the condition is satisfied, the compressor controls the compressor power supply to operate, and some advanced models are The engine computer directly controls the compressor power supply (with compressor relay). In addition, while the compressor is working, the engine should be speeded up, while some models have a speed-up valve in parallel with the compressor power supply; while some models are speed-controlled by the engine computer-controlled idle speed control valve. In addition, the blower and condenser should work simultaneously.

2.2 blower control circuit

This circuit controls the compressor operation, the compressor can work when it is running, and some models control the blower to work at the same time when the compressor is working. Of course, the blower can also work alone.

(1) The different speeds of the blowers in the manual air conditioner realize the shifting by connecting different resistors in series. The general switch controls the ground end of the blower, and the highest resistance does not string resistance.

(2) In the automatic air conditioner, it is controlled by the power triode. The control principle is that the base potential of the triode is controlled by the air conditioner computer to change the collector potential, so that the blower can obtain different rotation speeds. Most models also have a line that feeds back to the air conditioner computer, while some models have no feedback. Some models are combined with a crystal triode and a variable speed resistor at the same time, with both manual and automatic functions.

2.3 condenser fan control circuit

The condenser circuit is simultaneously controlled by the air conditioning operating state and the engine water temperature. The condenser fan must be operated as soon as the compressor is in operation. Air conditioning condensing fans are generally controlled in conjunction with engine radiator fans. Different manufacturers use different control methods depending on the air conditioning status and engine water temperature. The same manufacturer models have different control depending on the year, but there must be similarities. When analyzing the circuit, the circuit is divided into several different states for analysis.

(1) If the air conditioner is not turned on and the engine water temperature is low, the fan generally stops working.

(2) The temperature of the air conditioner is not high, the fan runs at high speed, and some models are operated at two speeds.

(3) The temperature of the air conditioner is low, and the two fans are running at a low speed (such as the Toyota series). There are also some models where the two fans start at the same time and operate at high speed, such as the Honda series.

(4) The air conditioning pressure is high, the water temperature is high, and the two fans must run at high speed, such as the Toyota series.

(5) Different working modes of the fan are different, and the water temperature switch is directly controlled by the pressure switch, such as the Toyota series. Some have water temperature sensors and pressure sensors that are controlled by engine computers or air conditioner computers, such as the Universal Buick and Mercedes series.

2.4 damper mode motor control circuit

There are generally three control systems for the damper motor.

(1) Intake mode damper motor, the control is usually three-wire or five-wire, one of the three-wire type is the power line, and the other two are the grounding line of the air-conditioner switch to control the forward and reverse, that is, the inner and outer circulation. Two of the five-wire type are the control lines of the two-way motor. This mode changes the polarity of the power supply, that is, it can change its steering, and the other three are position sensor lines. They are 5V power lines, ground lines and signal lines.

(2) Hybrid damper motor, there are many kinds of control circuits. Different models use different control circuits, one of which is the above five-wire type, the other five-wire type is three-position sensor, and the other two lines are 12V power supply. Line, one is the signal line of ECU control 0-5V; there are 7 lines, 3 lines are position sensor lines, the two lines are 12V line and ground line respectively, the other two lines are ECU control ground line; It adopts CAN-BUS data bus control, which is 3-wire type, which are 12V power line and ground wire and 5.5V control signal line.

(3) Airflow mode throttle motor control circuit. This circuit motor assembly has built-in sensor, microchip and position switch; 5-position type with position sensor (same as before), built-in microchip from CAN-BUS data bus 3-wire type (same as before); with position switch and IC chip 7 line Two of them are 12V power lines, one is a ground wire, and the other five lines are five modes to control the ground wire.

2.5 sensor circuit

This type of is relatively simple, the general public connection is grounded, and each signal line inputs the signal into the computer.

2.6 panel control circuit

Generally, it is A/C switch circuit, blower switch circuit, air flow mode switch and indicator circuit. In this circuit, you should pay attention to some important signal lines to the computer, such as A/C switch signal line, blower signal line, etc.

3 car air conditioning control circuit typical fault case

A Nissan-style A32 car cooling is not normal to the factory for maintenance. According to the owner's report, the car was repaired in another factory. At that time, the repair failure was that the compressor did not work. The repairman determined the cause of the fault through various aspects. After the circuit was modified, the compressor could work, but the refrigeration was not normal and no refrigeration was started.

Open the hood and find that the line to the electromagnetic clutch of the compressor is retrofitted, and the line is directly connected to the air conditioning control panel, controlled by the A/C switch. The power supply has the ignition switch to supply the supply, remove the modified circuit and restore it, according to the panel A. /C switch, the compressor does not work.

Diagnosis: Check the circuit schematic of this car. This car controls the compressor electromagnetic clutch controlled by the engine computer, components, compressor relay, engine computer, triple pressure switch, temperature controller, blower switch, A/C switch.

Inspection process: After opening the No. 1 relay, check the compressor relay. When the artificial grounding compressor can be sucked, the compressor circuit is all normal, and the ECM input terminal is checked for grounding, and the compressor can work, indicating that the ECM control is normal. Check the triple pressure switch, its function is to disconnect the compressor when the system pressure is too high, to protect the function. When the pressure is normal, it should be turned on. Check the terminals 1 and 4, and the continuity indicates that the pressure switch is normal. Check the function of the temperature controller to detect the surface temperature of the evaporator. When the temperature exceeds the bottom, the compressor is turned off. Otherwise, when the temperature rises to the set value, the compressor is turned on, the blower switch and the A/C switch are turned on, and the measurement No. 1 is performed. The terminal is 12V normal, the 3rd terminal 12V is abnormal, the 2nd terminal 0V is normal, the 2nd is 0V, the button control unit is controlled normally, and the grounding signal input by the blower is also normal. The possible reason is that the temperature controller or the evaporator temperature sensor is defective. Check the evaporator sensor circuit. There is an evaporator temperature sensor connector next to the evaporation box. It is found that one side of the evaporator is loose. After pressing, the blower switch and A/C switch are turned on. The compressor can work immediately and the engine can speed up. The fan is operating normally.

Due to the open circuit of the evaporator sensor, the temperature of the thermostat caused the temperature to be too low to cut off the line to the engine computer. The engine cuts off the compressor operation because there is no ground signal input. Since the compressor does not work, the air-conditioning fan does not work. When the temperature is high, the fan is controlled by the engine computer. In the vehicle maintenance, due to the unfamiliar control principle of the relevant line, the air-conditioning maintenance is a headache. It is not advisable. Only by understanding the control principle of the relevant lines, and clarifying the role and ins and outs of each line, can the fault be eliminated and the user can be effectively solved.

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