Oil pressure protection? High and low voltage protection? Thermal relay protection? Come and see if the automatic control appliance fails!
There are two types of failures in the automatic control of refrigeration devices: one is caused by the failure of the refrigeration system; the other is caused by automatic control, electrical component failure, and improper debugging. The following mainly analyzes the second type of failure.
Thermal relay failure
Thermal relay failure. Common faults of thermal relay include failure of the contact to cause the motor to start, the contact does not operate when the motor is overloaded, and the contact malfunctions when the motor load is normal.
① The motor cannot be started due to contact failure. The cause of the fault is generally the contact burnout, the deformation of the bimetal and the blocking of the action mechanism. When the temperature relay contact burns out, you can use fine sandpaper to polish the contact; when the bimetal is deformed, the bimetal should be replaced; when the action mechanism is jammed, the action mechanism should be cleaned and adjusted; if the fault is serious and the above method cannot be used to repair, it should Replace the thermal relay.
②The contact failure when the motor is overloaded is generally caused by the set value being too large. The set current should be reduced to clean up the dirt on the contact surface.
③When the motor is normal, the contact malfunction is caused by the fact that the set value is too small, and the action is not overloaded; the motor starting time is too long, the relay is tripped or started too frequently when starting, and the heating wire is subjected to large inrush current many times. Increase the set current value or replace with a suitable thermal relay.
AC contactor failure
①After power on, the contactor does not pull in. Check the solenoid coil. Use a multimeter to measure the two ends of the coil. If the resistance is zero, it means a short circuit, and if the resistance is infinite, it means an open circuit. All need to be replaced. If the contact action fails or is jammed by other parts, it should be adjusted carefully to eliminate obstacles. If the armature is stuck and cannot be raised or lowered, it should be removed and repaired in time.
②The contactor does not disconnect the contactor contact adhesion after power off. Check carefully to eliminate the adhesion failure, repair or replace the contact; if there is oil or dust on the surface of the contactor iron core, clean the iron core surface to make it flat, but do not Too smooth to prevent delayed release; the mechanical part of the contactor is jammed, and the jamming phenomenon should be eliminated; the reaction force of the return spring is too small, and the spring should be adjusted or replaced.
③There are many reasons for vibration or excessive noise during operation. Among them, when the end faces of the moving and static iron cores are in poor contact, try to repair them; if the contacts are oxidized, uneven, and burrs, use fine sandpaper and files to repair; such as contacts If it is burnt, you can replace it with a new contact, and check the cause of the burn; the vibration and noise caused by the excessive spring reaction force should be replaced with a suitable spring.
④The contactor moves slowly. When the coil voltage is insufficient, the coil voltage should be adjusted; when the reaction force of the return spring is too large, a suitable spring should be replaced; when the gap between the moving and static iron cores is too large, the gap can be adjusted smaller.
⑤When the contact is working, it will be fired. When the iron core is attracted and vibrated, the coil voltage can be adjusted to make it work normally; when the short-circuit ring is damaged, it should be replaced with a new one; due to frequent operations, contact deformation causes poor contact or contact force When it is insufficient, the burned contacts should be smoothed with fine sandpaper, the spring should be adjusted or replaced, and the contact gap should be readjusted.
⑥ The contact is seriously hot. When the load current is too large, find out the cause of the overload and take measures; when the contact is oxide or severely burned, which causes the contact surface to shrink and the contact is poor, use a file or sandpaper to repair.
Pressure controller failure
① The main reasons for the set pressure fluctuation are spring deformation, air leakage of the bellows or rupture of the connecting tube, and the displacement of the micro switch. This can be ruled out by adjusting or replacing the spring, repairing leaks, and adjusting the switch position.
②The high and low pressures are normal, and the controller is blocked because of the reasons. After the high and low pressure control terminals are activated, the manual reset switch is not pressed. When the pressure returns to normal, the contact will not automatically reset. You can press the reset switch to reset the contact; If the contact is severely burned out, you can polish the contact with fine sandpaper. If the contact is too damaged and cannot be repaired, replace it with a new one.
If the high and low pressure transmission rod is stuck, the cause of the jam should be found and eliminated; the low pressure air cavity leaks, at this time the pressure in the air cavity is reduced, the transmission rod moves down, the contact jumps out, and the refrigeration system will appear cooling If there is any leakage of the agent, find out the leakage point and repair it, or replace it with a new pressure controller; if the spring pressure is not adjusted properly, readjust the pressure of the spring; the lead wire of the high and low pressure switch is unsoldered, the controller can be disassembled to find out the broken Thread part and reconnect it.
③ The high and low pressure exceeds the normal range, and the controller does not operate due to the adhesion of the high and low pressure control contacts, improper adjustment of the spring pressure and the transmission rod. When handling, refer to the above methods to repair. It may also be due to air leakage in the air cavity of the high-pressure end. At this time, the pressure in the air cavity is reduced, and the transmission rod cannot be pushed to move the top contact. At the same time, the refrigerant in the system will leak. The leak should be found to be repaired or replaced .
Oil pressure difference controller failure
The failure of the oil pressure difference controller is mainly caused by the failure of the regulating spring, the electrical short circuit, the inaccurate pressure scale and the failure of the delay mechanism. The treatment method is to adjust or replace parts. Solenoid valve failure, solenoid valve failure and damage during operation, have a lot to do with whether the installation is correct or not, whether the operating conditions meet the requirements, etc. In addition, long-term power-on during repairs or tests, frequent opening and closing, etc. will also cause damage, which should be paid attention to.
①The valve does not move after power on: a. Use a multimeter to measure whether the power supply voltage meets the requirements. The operating voltage of the solenoid valve cannot be lower than 85% of the voltage specified on the nameplate. For example, the coil operating voltage specified on the nameplate of the fluorine FDF solenoid valve: AC voltage is 36V, 220V, 380V, and DC voltage is 24v, 110V, 220V, etc. If it is less than 85%, the voltage must be adjusted to meet the specified standards. b. Use a multimeter to measure whether the coil is open or burnt. If the circuit is open, replace with a new valve or rewind the coil. When rewinding, measure the diameter of the enameled wire and record the number of turns.
②The main reason for the valve core to be stuck or rusted and stuck by oil is that the filter in the drying filter installed in front of the valve is broken, and the desiccant and dirt enter the solenoid valve and mix with the refrigerating oil to form a paste oil. Most of the solenoid valves used in the water system are not used for a long time or cleaned irregularly, and the anti-rust layer is damaged and severely rusted. For this kind of failure, when the solenoid valve is energized, you can use a wooden stick to carefully knock the valve body from bottom to top, which sometimes works. If the fault cannot be eliminated, it must be removed and cleaned. The DF relay solenoid valve is an indirect opening and closing solenoid valve. When it is stuck, the regulating valve can be rotated up and down, and the dirt may be removed after repeated several times. The corroded valve core must be removed and cleaned, and the anti-rust layer should be re-plated in severe cases.
③The solenoid valve is not closed tightly: a. If the solenoid valve is not installed perpendicular to the pipeline, the valve stem is easily blocked when the valve core is dropped, resulting in loose closing. When repairing, the parallel pipeline can be adjusted to ensure that the valve body is perpendicular to the pipeline. b. If the valve core and valve seat are worn for a long time, the solenoid valve must be replaced when there is a gap in the sealing part. c. When the DF relay solenoid valve is not closed tightly, it may be that the gap between the float valve and the valve body is too small. The gap should generally be between 0.03 and 0.05mm. When the valve needle is closed, it enters the upper cavity of the float valve. The liquid is reduced, and the float valve is not easy to close the valve hole by its own weight. According to experience, an auxiliary small hole of 0.6～1mm can be drilled on the lower end of the float valve to make it enter the liquid. Note: When drilling a hole, the test should be carried out first, and then the larger one. If too much fluid enters when a hole is too large, the pressure difference between the upper and lower float valves will decrease, and the solenoid valve will not be easy to open. For solenoid pilot valves and main valves, the causes and troubleshooting methods are similar to solenoid valves.
Safety valve and check valve failure
① The safety valve failure will cause the safety valve setting pressure to shift due to the loosening of the regulating rod and the deformation of the spring; and the loose closing is caused by the valve core being stuck by debris and the valve core being damaged. The troubleshooting method is maintenance, replacement of parts and cleaning channels.
②The check valve is not closed tightly because the valve core is stuck by debris and the valve core is damaged. The troubleshooting method is maintenance, replacement of parts and cleaning channels.
Thermostat failure
①The main faults of the temperature bulb type thermostat are the improper installation position of the bulb, the leak of the bulb and the pipe, the damp or corroded micro switch, and the insensitive action. The treatment method is correct installation, leak detection repair, maintenance switch, etc.
②Failure of the mercury thermometer with electric contact: a. Set temperature changes. This is caused by the malfunction of the electronic relay (signal amplifying relay) used with the mercury thermometer. The treatment method is to repair or replace the electronic relay. b. Temperature control failure. The main reasons are damage to electronic relays; broken glass rods; electrical corrosion of the contacts caused by the control current exceeding the rated current of the electric contact thermometer; or the temperature of the controlled medium is too high, exceeding the maximum scale line of the thermometer, causing the mercury column to be interrupted, etc. . The treatment method is to replace the parts, repair the contacts, repair the mercury column, etc.
Level sensor failure
① The reason for the sluggish or no signal of the liquid level change signal is that the refrigerating oil enters the liquid balance pipe; the sealing performance of the cable compartment is not good, which makes the cable package damp or corroded and damaged; the components in the electrical control box malfunction. The treatment method is to remove the refrigerating oil in the pipe, check the line package and control box, and replace the components.
Picture 8
②The liquid level change signal is sent out too frequently. The specific reason is that the adjusted upper and lower liquid level difference is too small; because the refrigerant in the shell evaporates violently, the floating ball keeps beating and causes the false signal to be sent. The treatment method is to adjust the liquid level and eliminate the gas.
