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Air Conditioner, Refrigeration, Electrical and Ventilation system failure analysis

First, overview

Air conditioner by refrigeration system, electrical system and ventilation system and other parts of the operating state and the working environment has a close relationship, so the fault analysis of the air conditioner needs comprehensive consideration. The refrigeration process is as follows:

Second, the preparation before the overhaul

1. Understand the occurrence time and condition of air conditioner failure, and whether there are external factors.

2. the air conditioner should be checked in operation (except for not running), so that it is fully exposed to symptoms.

3. do not be too hasty underground conclusion, proceed to repair, but to check carefully, after thinking repeatedly and then repair.

Third, the failure analysis of refrigeration system

(a) refrigeration system pressure and temperature measurement: in addition to the deterioration of indoor and outdoor ambient temperature, operating pressure and temperature beyond the normal range, there must be a fault, which is a very important basis for judging the cause of the fault.

1. the pressure of the refrigeration system: refers to its suction pressure and exhaust pressure;

(1) The suction pressure is the pressure of the compressor suction port, but the measurement means are difficult; Because the pressure difference between the suction tube and the suction mouth is small, the pressure at any place on the suction tube can be used as the suction pressure, and the suction pressure is close to the evaporation pressure.

(2) exhaust pressure refers to the pressure of the compressor exhaust port, for the completely closed compressor, before the capillary, the pressure at any place on the gas pipe can be used as the exhaust pressure.

2. the temperature content of the refrigeration system: evaporation temperature, suction temperature, condensing temperature, exhaust temperature, infusion temperature, etc., and the system plays a decisive role in the evaporation temperature and condensation temperature. The above temperature can be found only by measuring the pressure and checking the thermodynamic property table of the working medium.

2. the influence of inspiratory pressure change on the system

When refrigeration is running, the suction pressure is closely related to the evaporation temperature and the circulation amount of refrigerant; For the system with capillary as throttling, the suction pressure is related to the condensing pressure, refrigeration dose, compressor efficiency, and refrigeration load, so when checking the refrigeration system, the pressure gauge should be installed in the suction pipe section, and the suction pressure can be read to provide an important basis for fault analysis.

(1) The inspiratory pressure is lower than the normal value, and the reasons are: the refrigeration dose is small, the cold load is small, the condensing pressure is low and the filter is not smooth.

(2) The suction pressure is higher than the normal value, the reasons are: excessive refrigerant charging, large refrigeration load, high condensing pressure and poor compressor efficiency;

3. when the refrigeration system is running, the exhaust pressure corresponds to the condensing temperature, and the condensing temperature is related to the flow rate and temperature of the cooling medium, the injection amount of refrigerant, the efficiency of the compressor and the cold load. When checking the refrigeration system, a pressure gauge can be installed on the exhaust pipe to read the exhaust pressure as an analysis of fault data.

(1) The exhaust pressure is higher than the normal value, the reasons are: low flow of cooling medium or high temperature of cooling medium, excessive refrigerant charge, large cooling load, etc.; The amount of refrigerant charging is large, and the excess refrigeration liquid occupies part of the condensing pipe, which reduces the condensing area and causes the condensation temperature to rise.

(2) The exhaust pressure is lower than the normal value, the reasons are: the compressor efficiency is poor, the refrigeration dose is less, the cooling load is small, the filter is not smooth and the cooling medium temperature is low; These factors will cause the circulation of the system to decrease, the condensation load is small, so that the condensation temperature drops.

4. From the above inspiratory pressure and exhaust pressure changes, the two are closely related. In general, the suction pressure is high, the exhaust pressure is high; Low suction pressure, low exhaust pressure; This is the operation law of the refrigeration system.

(2) The impact of temperature changes on the refrigeration system:

1. the evaporation temperature and its suction pressure is corresponding to the condensation temperature is corresponding to the exhaust pressure, the analysis of the suction pressure and exhaust pressure changes, is equal to the analysis of the evaporation temperature and condensation temperature changes.

• The suction temperature is closely related to the exhaust temperature, that is, the suction temperature is high, and the exhaust temperature is correspondingly increased, and the reverse is low. The suction temperature is related to the flow rate of the system, the flow rate is larger, the suction temperature is lower, and the reverse is higher.
• For th capillary system, the inspiratory temperature is related to the amount of refrigerant injection, the refrigeration dose is more, the inspiratory temperature is low, and the reverse is high. The exhaust temperature is related to the condensing temperature, the condensing temperature is high, the exhaust temperature is high, and the reverse is low.

2. condensing unit components of the surface temperature changes on the impact of the system

These temperatures are difficult to measure with a thermometer, use the feel to estimate its temperature range, and then judge whether the temperature is normal or not.

• The impact of the compressor housing and exhaust temperature changes: in summer, the compressor exhaust temperature should not exceed 130 °C, exceeding this temperature is abnormal.

The ultra-high exhaust temperature is caused by the ultra-high suction temperature of the compressor. The consequence is that the frozen oil may form carbon, affecting the life of the compressor.  If the exhaust temperature is not hot, it indicates that the suction temperature is very low, and the compressor runs in case of little refrigerant, which will affect the heat dissipation of the motor winding and accelerate the aging of the insulating material.

• The influence of the temperature change of the condenser heat pipe: under normal circumstances, the front half of the exhaust pipe is very hot, and the heat sensitivity of the back half of the heat pipe is greatly

reduced than that of the front half, which is because the refrigerant in the back half pipe has gradually liquefied, reaching the condensing temperature and subcooling temperature.

Under abnormal circumstances, one is that the first half is not too hot, and the second half is close to the ambient temperature, mainly because the compressor inhales the liquid refrigerant or the cold dose is less. The other is that the whole condensing tube is very hot, the reason is that the refrigeration dose is too much, the ventilation is small, or the ambient temperature is very high.

• infusion tube temperature: the liquid tube is warm.

Abnormal condition, the liquid pipe is too hot. The reason is that the condenser heat dissipation is not good, the condensation temperature is high or the refrigerant charge is too much.

• Filter temperature: the same as the liquid pipe;

Abnormal phenomenon is that the filter is cold. The reason is that part of the mesh of the filter is blocked, and when the refrigerant flows through the filter, there is throttling. There is also an abnormal situation that the filter is not hot, similar to the ambient temperature, the reason is that the filter is all blocked by sludge, and the refrigerant can not flow through.

• Suction tube temperature: under normal circumstances: suction tube feel very cool, and dew.

Abnormal situation, one is that the suction tube is too cold, too much dew, so that the pump shell large area condensation. The reason is that the refrigeration dose is large, the liquid can not be fully vaporized in the evaporator, and there is liquid reflux phenomenon. The harm is that the compressor may carry out wet stroke operation, serious liquid strike will occur, and the valve disc is threatened. The second is that the suction pipe is not cool, no condensation, and the pump shell is very hot. The reason is that the refrigerant flow is small or the refrigeration dose is insufficient, and the consequence is that the exhaust temperature rises and the cooling capacity decreases.

6, evaporation unit related to the impact of temperature changes on the system

• Capillary: capillary is very cool, and there is dew, there is liquid flow sound.

Abnormal situation: one is that the surface is very cool and dew is also condensation, but the flow sound is louder, and it is the flow of gas. The reason is that there is less refrigerant. The second is that the surface is not cool, there is no dew, and you can't hear the flowing sound. The reason is that the capillaries are blocked.

• evaporator temperature: normal conditions: the outer surface of the evaporator is very cold, its condensation beads continue to drop, and the temperature difference between the inlet and outlet wind is large, usually in 12-14 °C.

Abnormal conditions: the evaporator surface is not too cool, dew is not much, or no condensation, you can hear the flow sound is very loud, and the temperature difference in and out of the wind is small. The reason is that the refrigeration dose is insufficient.

7. the impact of ambient temperature

• Outdoor temperature: generally exceeds 35 °C, the system operation may exceed the normal situation, mainly in the condensation temperature is high, exhaust temperature is high, cooling capacity decline, followed by the result is caused by overload operation.

When the temperature exceeds 43 °C, it has exceeded the critical point of safe operation of the air conditioner, which will lead to the action of the electronic protection device and cut off the power supply. If you want to force operation, the consequence is to shorten the service life of the air conditioner.

• Indoor temperature: the normal constant temperature does not exceed 30 °C.

If the evaporation unit runs above 30 °C for a long time, the air conditioner will run under overload for a long time, and the condensation temperature and exhaust temperature of the outdoor unit will rise. Will lead to overheating over current protector action, cut off the power supply.

8. heat pump system: the operation is the same as the single cooling condition, the heat pump mainly checks the working condition of the reversing valve; The reversing air flow of the reversing valve, the electromagnetic valve suction sound, the reversing valve is faulty, it can not be used for heating operation, generally only replacement.

Four, fully enclosed compressor failure analysis: because the spare parts are difficult to buy, even if the motor burns out the heavy winding coil, it is difficult to guarantee, therefore, the general replacement of the compressor.

(a) When replacing the compressor should pay attention to:

1. should be the same model of the same specifications of the compressor. If there is no press of the same model, its main performance specifications should also be the same or close. The main performance includes the refrigerating capacity under the same working conditions, the voltage, phase frequency, current, etc., and the capacitance of the capacitor.

2. the overall size should be the same or equivalent, the foot size should be the same. If you can not buy the same foot size of the compressor, you need to modify the foot of the air conditioner chassis.

3. the direction and position of the suction and exhaust pipe should be the same or close. If they are not the same, an important new arrangement will take over.

(2) Fully enclosed compressor prone to failure:

1. poor refrigeration efficiency: refers to the actual displacement of the compressor decreases, can not reach the nominal cooling capacity of the product calibration, can not meet the original cooling load. Poor refrigeration efficiency is generally caused by the following two factors:

• serious wear of piston and cylinder: the gap between piston and cylinder is quite strict, and there is a layer of oil film in the gap to lubricate and seal. If the gap between the piston and the cylinder is large, the oil film will be disconnected, resulting in gas leakage; If the clearance is too small, it will produce melting (holding) or starting difficulties. When the piston or cylinder is seriously worn, when the piston compresses and exhausts, a part of the gas in the cylinder leaks into the pump housing through the gap, so that the exhaust volume is lost, and the compressor cannot reach the original exhaust volume.

• Serious leakage of the air valve: when the suction and exhaust valves on the valve plate are not sealed with the valve line on the valve plate, there is a gap. When it is suction and exhaust, a part of the gas will leak back from the gap, causing the loss of the exhaust volume of the compressor. The production factors are as follows:

A, the system is not clean, there is sludge mixed in the refrigerant flow, sludge sticks to the valve line and valve plate, hit by the valve plate, accelerate the valve plate and valve line wear, its sealing gradually weakened.

B. the exhaust temperature is often too high, so that part of the frozen oil gradually carbon, stick to the valve structure, destroy the valve sealing.

C. the system often occurs mild liquid strike, the valve plate is gradually deformed or damaged by the impact of the liquid, or aggravate the wear and weaken the sealing of the valve structure. The valve plate has been severely hit by liquid, the valve is damaged, and the valve plate is broken, and the sealing is seriously damaged. The symptoms of the above situation are that the exhaust pressure drops, the inspiratory pressure rises, the suction and exhaust pressure difference is small or small, and the serious is almost zero; Under normal circumstances, the difference in pressure is very large, the pump shell has different degrees of heat, and some exhaust pipes are very hot.

2. the compressor is not running: when the compressor power supply, only hear the pump shell machine has a "buzzing" sound, but not running, about 3-5 seconds time, thermal protection jump, cut off the power supply. This symptom is caused by the following faults: the compressor is less oil, poor lubrication, the cylinder, the motor is not moved.

3. compressor motor damage: symptoms are: when the power is switched on, the fuse is blown or the air switch trip. This symptom has the following three kinds of failure:

• Because the motor stator winding is burned out, the insulation layer of the electromagnetic coil is scorched, the insulation is destroyed, and the winding touches the shell. The cause is that the air conditioner is overloaded for a long time, and the protector fails, so that the winding works for a long time under the condition of superheat, the insulation gradually aging, and finally the insulation layer is destroyed.

• inter-turn short circuit makes part of the coil insulation in the stator winding of the motor be broken down and part of the coil touch the shell. Cause: stator winding or assembly, the local electromagnetic coil is slightly damaged, after running for a period of time, the scar spread and breakdown insulation.

• Touch the wire, the motor power supply wire insulation is damaged or cut off and touch the shell. The insulation layer of the stator winding of the motor is seriously aging, but it has not been burned out. Its symptoms are a little different from the above, that is, it can run for I-2 minutes, and then also burst the fuse, or the air switch trip, and the current is very large. The reason for this is the same reason that the winding burns out, and this motor does not work.

4. Abnormal noise during operation: the internal parts of the pump shell collide with each other after relaxation, generally the exhaust pipe touches the pump shell, the bearing is worn out and causes the piston to knock the valve plate, as well as the stator and rotor friction, electromagnetic noise of the motor.

Fifth, electrical system fault analysis

• The electrical control of the air conditioner: strong current line control board and electronic line control board; Electrical equipment is to control and protect the refrigeration system and fan system of the device,

in addition to the electrical line itself failure, there are a considerable part of the failure in the refrigeration system and fan system, but its symptoms are reflected from the electrical control.

• The phenomenon of strong current control system failure

1. compressor and fan do not operate:

• No power supply; The power socket is disconnected; Poor plug socket contact;
• the connector contact is poor, the fuse of the control line is blown, and the internal break of the switch is selected;
• the power supply voltage is too low, the motor can not start, and then the thermal protector jumps and cuts off the power supply;
• the electrical control line is broken. There are improper operation, quality problems, refrigeration system and fan system caused.

2. the fan is running but the compressor is not running

• The overload protector contact is in the disconnected position, because the refrigeration system is overloaded during operation, so that the overload protector jumps open.

• Compressor operation capacitor damage, may be usually improper maintenance or by the intrusion of moisture.

• The compressor motor is burned out.

3. after the operation of the air conditioner, the compressor starts and stops frequently:

• the installation position of the temperature sensing package of the thermostat is too close to the evaporator, so that it is transmitted to the evaporation temperature.

• The power supply voltage is unstable, high and low.

• The bimetal plate of the overload protector is in poor contact, resulting in the situation of power supply on and off.

4. the compressor running for a long time without stopping the cause of failure

• Due to the indoor heating body, heat, air conditioning room heat load is large, the air conditioner and the room do not match.

• Due to the rough surface of the contact, the contact in the thermostat will adhere and can not be disconnected.

5. heat pump type air conditioner does not heat

In the refrigeration operation is normal, and the heating operation is not heated, the electromagnetic reversing valve or switching switch is faulty.

• The solenoid valve coil is burned out or broken, the reasons are: working in a harsh environment; Coil stop, open frequently; Long-term work under abnormal voltage, resulting in coil often in overtemperature work, insulation aging breakdown.

• The spool in the solenoid valve is stuck or damaged. The reasons are: sludge into the valve and block the spool; Poor quality, short service life.

• The reversing valve can not be reversed, the main reason is that the refrigerant is not clean and manufacturing assembly problems, flexible plug can not run.

• Hot and cold switch failure, the reason is that the mechanism is damaged, the surface of the contact is oxidized and not conductive.

6. the shell has leakage phenomenon, hemp electricity, the reason is:

• The insulation performance of some electrical appliances is reduced or affected by moisture;
• the grounding wire is poorly grounded or not grounded.

(2) The fault phenomenon of the electronic line control system: the control board part is a low voltage control line, and its control voltage is 5V, 9V, 12V or 24V. It is characterized by safety and reliability, control functions, small size, compact control panel, beautiful.

1, the air conditioner no action after the boot: when the forced operation key is pressed, the air conditioner does not act, there is no sound, the power supply is not switched on, can be checked in the following order:

• There is no power in the power line: check the electrical appliances that control the power line, such as the knife switch or the air switch, whether to cut off the power supply.

• The power supply is out of phase. The power supply source is the three-phase air conditioner, and the three-phase power grid has the possibility of one or two phases losing power.

• The fuse of the control board of the indoor unit is blown or the varistor is damaged. In order to prevent too high voltage or too much current into the control line, protectors are generally installed, once there is a high voltage or large current into the control line before cutting off the power to protect the circuit board.

• The connector is in poor contact.

• The key switch is damaged, the running key contact is poor or the key parts are damaged.

• The circuit or electronic components on the electronic control board are damaged, so that the control board is out of control, and the circuit of the electric control board should be measured.

2. after starting, the indoor fan runs, but the compressor does not run, and the fault light flashes; Check according to the fault guide:

• The power supply is out of phase or the voltage is too low, to check the power line and measure its voltage value is too low.

• If the compressor current is overloaded, check whether the thermal protector on the compressor pump housing is jumping. Usually when the compressor overload after the current is too large, the thermal protector to jump; Three-phase motor protector is buried in the motor winding in the pump shell, regardless of the single-phase and three-phase power supply motor, can be in the compressor pump shell junction box with a multimeter resistance to measure whether the winding is through, if not, the protection has been off the power supply, and so on about 5 minutes will generally recover, and then check the cause of overload when running.

• Outdoor fan overheating or thermal protector damage, fan overload operation, the winding temperature rise is too high, the thermal protector will jump and cut off the power supply, you can check whether the fan inlet connector is through. If it is not possible, the thermal protector will jump and recover after cooling. If it is not restored, the thermal protection may be damaged, and the thermal protector should be identified.

• The connector is in poor contact. The wiring of the fan motor is generally inserted with connectors, which may produce poor contact. In addition, check whether the connection in the compressor pump shell junction box is loose and poor contact.

• The AC contactor coil is broken, the contact can not be closed, and the motor has no power to enter.

• The electronic control board is damaged.

3. the air conditioner will stop soon after start, can not continue to operate, and the fault light is also flashing; According to the fault guide check:

• The exhaust pressure is too high.

• Inspiratory pressure is too low.

• The fan motor is burned out.

• Compressor overcurrent overheat protector action jump.

4. The power indicator lights up after the startup, the indoor fan runs, but the compressor does not run; It indicates that the refrigeration system and the fan system have no fault, but the wrong operation and the temperature control switch are faulty, so the fault indicator does not blink.

• Select the air supply mode, just dial the cooling mode.

• The temperature does not reach the set value. When the temperature setting value of the thermostat switch is higher than the room temperature, the contact of the thermostat is always open, the refrigeration system will not operate, and the temperature value should be reset.

• The sensor of the thermostat - thermistor is damaged, so that the compressor protector temperature control is out of control. A multimeter can be used to measure its resistance value and the corresponding resistance value of temperature to identify its quality.

Six, the failure of the ventilation system is manifested in three aspects: the air volume decreases, the motor does not rotate, and the noise is large during operation.

• Decrease in air volume

1. the tightening screw of the wind wheel is loose: when the motor is running, the impeller is slipping and idling, in this case, the air volume decline is quite obvious.

2. wiring error caused by motor reversal, impeller reversal;

3. the filter is dirty and blocked: the flow resistance of the air will increase, so that the air volume will decrease significantly.

4. condenser dirty blocking: heat sink dust blockage, air volume will also decrease significantly.

• The motor can not be turned

1. bearing serious wear: the rotor and the stator unilateral friction, the symptoms of the motor is buzzing, do not move or the speed is quite low, the current rises. If the power is cut off, rotate the motor shaft by hand, there is a heavy and heavy feeling, and there is friction sound.

2. motor winding burned out: use a multimeter to measure the insulation of the winding has been broken down, and touch the shell; After the fault occurs, electric control protection.

3. winding turn to turn short circuit: the measurement resistance should be significantly reduced, the symptom is that the running current is large, the operation of the moment to blow the fuse.

4. The motor sliding bearing is burned, and the shaft can not be turned by hand.

• The running noise is large

1. impeller and wind ring friction: metal collision sound, the reason is that the fastening screw is loose, so that the impeller displacement phenomenon.

• The bearing is seriously worn, but it can still run, and the shaft pulsates when it runs.

• The bolt of the motor base is loose and makes a jitter sound.

終了！