Common faults and maintenance of car air conditioners

In order to meet the passenger car on a hot day, giving passengers a comfortable and cool cabin environment, air conditioning has become an indispensable part of the passenger car. With the maintenance of air conditioners, the problems of air conditioners are becoming more and more prominent.

1 Common troubleshooting of automotive air conditioning systems 1) Air volume control. The reason why the blower does not work: the ignition power supply circuit is open or shorted; the air volume control switch is faulty; the line connector is in poor contact; the blower is damaged. Use a multimeter to detect fault points for repair or replacement.

The blower air volume is only caused by the high speed gear and the low speed gear: the control switch fault and the air conditioner blower ballast resistance fault. Repair method: repair or replace after finding out the cause.

Insufficient air volume Possible cause: The blower motor bearing is damaged; the resistance value of the line or motor coil exceeds the specified value, the resistance is too large; the evaporator is dirty and blocked, so that the airflow cannot pass smoothly. Maintenance method: Repair and replace after finding out the cause. Clean the evaporation tank.

2) Temperature control. The reason why the air conditioner compressor cannot be started is as follows: there is no refrigerant in the system or the low pressure is lower than 0.2 MPa, and the high pressure is higher than 2.65 MPa. Inspection method: The pressure inside the refrigeration cycle system can be detected by using a special pressure gauge. If the set value is not met, adjust, leak or replenish the refrigerant.

Circuit failure or compressor electromagnetic clutch failure; evaporator air outlet temperature is lower than the set value or temperature sensor failure; engine water temperature is higher than the set value, the acceleration switch is turned on, and the engine speed is lower or higher than a certain set value; Idle speed increase solenoid valve failure, etc. If it is a circuit fault, the cause can be found for repair. If it belongs to the air conditioner control switch and each sensor is faulty, it needs to be replaced.

Although the compressor works but the cooling effect is not good: the refrigerant leakage causes the pressure in the system to be low, and the special pressure gauge can be used to detect the high and low pressure in the system. If the pressure is low, the leakage can be measured by means of vacuuming or the like through an electronic leak detector. The use of an electronic leak detector is simple, and it can reflect the leakage of the refrigerant by the size of the buzzer sound. The vacuum gauge can be used to observe the needle of the vacuum gauge. If there is a leak, the needle will suddenly rise when it drops to a certain position, and this is repeated. The higher the value of the needle back negative pressure, the lighter the leakage, and vice versa. Key detection parts: joint parts of parts that have just been dismantled and repaired; compressor oil seal, front and rear end cap seals; condenser, oily parts on the evaporator coil; expansion valve fusible plugs and connection points of various pipelines.

The condenser fan does not turn into a high-pressure gas refrigerant that cannot be cooled during the condenser cycle, and the heat exchange capacity is poor, so that the refrigerant entering the expansion valve cannot completely form a liquid state. The liquid storage dryer filter is too dirty or the inclination is too large when installing; the expansion valve is blocked by ice or the evaporator is too dirty, so that the airflow cannot pass smoothly, resulting in poor heat exchange capacity; the compressor electromagnetic clutch gap is too large or the drive belt passes. Loose, causing the compressor to slip and slip.

The reason why the compressor does not stop: short circuit between the control circuit and the power supply; the air temperature sensor of the evaporator is faulty; the electromagnetic clutch of the compressor is faulty. Repair or replace after identifying the cause.

The high and low pressure of the system indicates that the number is too small, and the cooling effect is poor: the expansion valve has poor throttle effect, and the pressure adjustment screw is improperly adjusted; the deformation of the intake air check valve in the compressor is not tight, and there is refrigerant in the compression process. countercurrent.

2 Automotive air conditioning refrigeration troubleshooting The normal operation of the air conditioning system, the temperature of the air outlet should be between 0 ~ 5 ° C, at this time the temperature inside the compartment should be maintained between 20 ~ 25 ° C (outside temperature is about 34 ° C). All factors that can reduce the flow rate of the refrigerant at the outlet of the expansion valve and all the factors that can cause the temperature and pressure on both sides of the high pressure and low pressure in the system to exceed or fall below the standard value will result in insufficient cooling capacity of the system.

The amount and quality of refrigerant and refrigerating machine oil in the system should be checked: if there is too much refrigerant, the excess refrigerant should be slowly released from the low pressure side; if the refrigerant is insufficient, in addition to the appropriate amount of replenishment, the refrigerant should be identified. The reason for the lack and the corresponding maintenance measures. Check the amount of refrigerating machine oil injection. If it is too much, discharge the excess part; check the quality of the refrigerant and refrigerating machine oil. If it is too dirty, it will block the filter screen and the evaporator cooling core tube and system piping. At this time, the dirty refrigerant and the refrigerating machine oil should be discharged. After cleaning the whole system, the refrigerant and the refrigerating machine oil are filled, and the liquid storage drying filter is replaced and the expansion valve is cleaned with anhydrous alcohol; the refrigerant and the refrigerating machine oil are inspected. If there is too much water, it can be treated according to the “system excess water” failure; if there is air in the inspection system, it can be handled according to the “air in the system”.

Mechanical maintenance: check the compressor cylinder, piston, exhaust valve and so on. If the actual displacement of the compressor is reduced due to excessive wear or damage, the compressor should be repaired in time; check the compressor drive belt. If it is too loose, adjust its tension; check the compressor coupling. If it is loose, it should be Adjust to normal; check the electromagnetic clutch: the joint between the pressure plate and the pulley is seriously worn or oily, and the battery voltage is too low, etc., which will cause the clutch to slip. At this time, the fault should be handled according to the “clutch slip”; check the condenser and clear it. The dirt on the surface, correct the curved fins; adjust the tension of the transmission belt of the cooling fan; if it is checked that the fan does not turn, the fault should be handled according to the "condenser fan does not turn"; if the fan speed is too low, it should be checked The high-voltage switch that controls the fan speed should be replaced if it fails. Check the evaporator. If there are dust and debris on the surface, it must be removed and the blockage in the air duct must be removed. Check the expansion valve and temperature sensor package: If the expansion valve opening is too large, the expansion degree of the expansion valve should be adjusted; if there is leakage in the valve head or the temperature sensing package, the expansion valve should be replaced; if the temperature sensor package is not installed correctly, and the evaporator If the contact at the mouth is not good and the insulation layer is loose, the package should be adjusted after the temperature package is installed. Check the storage device. If the blockage occurs, it should be replaced. Check the dry filter. If the blockage occurs, it should be replaced; check The air conditioning amplifier should be repaired or replaced if it is faulty.

3 Automotive air conditioning typical failure and troubleshooting Automotive air conditioning system failure generally has the following aspects: no refrigeration or poor refrigeration; abnormal sound or noise; can not control or electrical components failure; engine overheating and power shortage. Common methods for analyzing faults generally pass through four aspects: listening, watching, touching, and measuring. Including automobiles, engines, compressors, evaporating fans, condensing fans and relays, when the air conditioning system is started and the compressor starts to work, the engine sound is slightly increased, which is regarded as a normal phenomenon.

Look closely at the car's instrumentation, pressure, water temperature, oil pressure and various performance indicators and signal indicators on the control panel of the air conditioning system. Whether there is leakage in the piping system, observe the flow of refrigerant in the sight glass. Touch refers to the operation of the air conditioning system after a period of time, such as the temperature and air volume of the air outlet, the compressor exhaust pipe and the return pipe should have a significant temperature difference, the temperature at both ends of the dryer should be consistent, the expansion valve inlet is hot The exit is quite cold. Check the working condition by observing the sight glass mounted on the oil reservoir. Under normal conditions, it should be clear, no air bubbles and the evaporator air outlet is cold. If the air outlet is not cold, it means that the refrigerant has leaked; if there is air bubble in the liquid and the air outlet is not cold enough, it means that the refrigerant is insufficient, and it can be removed by the cooling method.

The fault is judged by touching the relevant part. Touch the high pressure circuit (from the compressor outlet D condenser D reservoir D expansion valve outlet) should be hot. If there is a significant temperature difference between a certain part or the outlet and the inlet, it means that the blockage is blocked here; touching the low-pressure circuit (from the outlet of the expansion valve D to the evaporator D compressor) should be colder. If there is no obvious temperature difference between the high and low pressure sides of the compressor, This indicates that the system has leaks or no refrigerant.

The test refers to testing the air conditioning system by means of a manifold pressure gauge, a leak detector, a multimeter, and the like, and finding out the fault. Listening means paying attention to the abnormality of the car air conditioning system.

The efficiency of any air conditioning system depends on the proper operation of the various components. Proper use and maintenance not only reduces unnecessary accidents and damage, but also increases the service life of the air conditioner.

1) No air conditioning can be produced. The fault phenomenon is to open the fan switch and the A/C switch. The fan works normally, but the compressor does not run; the fan switch is turned on, the fan does not rotate; the fan and the A/C switch are turned on, and the fan and the compressor are working normally, but not cooling.

The cause of the failure: the drive belt is too loose or broken; the compressor can not run; the compressor valve plate is not working well, the high and low pressures only change slightly during the shifting; the pipe is broken, the refrigerant leaks, no high pressure; the dry reservoir or The expansion valve is frosted and blocked; the melt is blown, the wiring is disconnected or disconnected, the cold air switch is damaged, and the fan motor does not work.

Troubleshooting: The air volume is normal, the compressor does not work. If the electromagnetic clutch is faulty, turn on the A/C switch and use the test light to detect the clutch power. If the test light is on, it indicates that the electromagnetic clutch is faulty. If the test light is on, check the electromagnetic clutch control circuit. .

If there is no air volume in the blower, first check whether the fuse is intact, and then check the working status of the fan switch and the fan relay; if the fan is normal, the compressor works, but does not cool, check whether the expansion valve is dirty, if it should be cleaned or replaced . Also check the operating status of the evaporator and reservoir.

It can be repaired by tightening or changing belts, changing melt pipes, repairing or replacing wires, switches and fan motors, repairing clutches and compressors or compressor valves, expansion valves and other measures.

2) Insufficient cooling capacity. The fault phenomenon is to turn on the fan and A/C switch, and use the thermometer to measure the temperature above the 5 °C or the inside temperature of the fan is higher than the normal adjustment temperature.

The cause of the failure is: the electromagnetic clutch of the compressor is slipped to reduce the output efficiency; the air volume in the air duct is insufficient or the refrigerant is insufficient, there is a bubble in the liquid mirror, the high pressure is too low; the fan motor is not working well, and the air flow around the condenser is not smooth. High pressure is too high.

Exclusion process: Observed from the sight glass, if there are bubbles every 1~2s, it indicates that the refrigerant is insufficient; if there are bubbles appearing from the sight glass, there is no liquid flow, and the high and low pressure sides are overheated. High high and low pressures indicate excessive refrigerant; a large number of bubbles are seen from the sight glass, indicating that there is air in the system. If the refrigeration system works for a period of time, the low pressure becomes vacuum, the expansion valve is frosted, the air is not cold, the machine stops for a while, the work is normal, and the above failure is repeated soon, indicating that there is moisture in the system. Poor operation of the condenser can also result in insufficient cooling capacity. Check if the speed of the condenser fan is too low, whether the condenser fin is blocked, whether the evaporator is dirty, if it is clean and clear the passage; replace the motor, electromagnetic clutch and compressor to eliminate it.

3) Intermittent operation of the refrigeration system. The fault phenomenon is that when the air conditioner is used, the cold air supply is discontinuously discontinuous.

Fault reason: temperature control is out of order; compressor electromagnetic clutch slips; electromagnetic clutch coil is loose or poorly grounded; there is moisture in the system causing intermittent expansion of the expansion valve.

Exclusion process: Check if the electromagnetic clutch is slipping; check whether the blower is running well in the circuit; whether the thermostat works well. If the thermostat is not working well, it will cause the air conditioner compressor to start and disconnect too frequently; the expansion valve ice block and the temperature sensor package will also cause the air conditioning system to work intermittently. It can be repaired by adjustment, repair and replacement.

4) The system noise is too large. Fault reason: internal wear of the compressor or loose mounting bracket; insufficient power supply voltage of the electromagnetic clutch or loose belt; fan motor loose or worn; too little refrigerant, “wind” sound or refrigerant charge at the inlet of the evaporator Many, the high-pressure pipeline has vibration sound, the compressor has hammering sound; the clutch slips.

Troubleshooting: You can tighten or replace the drive belt, tighten the bracket, replace the fan motor, compressor, increase the voltage, charge the refrigerant or release too much refrigerant.

5) The condenser has poor heat dissipation. The phenomenon is that the temperature of the air outlet is high, and the high and low pressure sides are both high. Check whether the condenser fins are blocked by dust or dirt, whether the fan is off the condenser, and the fan drive has no slip or looseness, and it should be excluded according to specific reasons.

6) Other failure analysis. Compressor pulley common faults: excessive refrigerant pressure, high pressure and excessive compressor load, causing the pulley to slip; the belt is too tight or too loose.

The car engine is overheated: the cooling water circuit is blocked; the radiator cooling air volume is insufficient; the condenser fins block the air volume.

Common faults of air conditioning condensers and common faults of fans: fouling of condenser pipes and heat dissipating fins will affect heat dissipation capacity, causing extreme pressure rise in refrigeration system; damage to condenser piping and joints; damage to fan speed control resistors; poor fan contact , affecting the speed of the fan; the fan relay is not working properly.

Failure of the liquid storage drying tube: The desiccant should be replaced when it reaches saturation; after the dryer is clogged, there is a significant temperature difference between the inlet and outlet.

Common failure of the expansion valve: the filling medium leaks in the temperature sensing package, causing the expansion valve to close and the refrigerant not to circulate. The phenomenon is that the refrigeration system is vacuumed just after starting the operation, the expansion valve does not have a little flow of sound; the filter at the inlet of the expansion valve is blocked. The phenomenon is that the suction pressure is low or vacuum. The temperature inside the car does not drop, and half or the entire expansion valve is hoarfrost, and the side ear listens to the expansion valve with a weak “吱吱...” intermittent sound, which means that the filter is not smooth, but not completely blocked, the expansion valve is throttled. The hole is blocked by debris. The expansion valve should be removed to remove the blockage. Carefully measure the adjustment screw with a deep vernier before removing it (this is because the adjustment screw has been adjusted to match the evaporator capacity at the factory). The installation temperature sensor should be close to the tail of the evaporator; there is moisture in the system, which freezes into ice at the expansion orifice and blocks the expansion valve passage. When the car refrigeration and air-conditioning system started running, its work was normal. After a period of time, its suction pressure dropped sharply and it showed a vacuum state, indicating ice blockage.

At this time, the expansion valve body is heated for 1 to 2 minutes, and the suction pressure can be instantaneously passed with the ascending expansion valve, so that the refrigeration is normal when the air conditioner is just turned on, but the cooling effect is gradually deteriorated soon, because the air conditioner is inspected for air maintenance. When water vapor remains in the system. At this time, it can be cleaned with clean nitrogen, or the desiccant or the liquid storage dryer can be replaced, and then evacuated twice and refilled.