1. See if it works. If the contactor is engaged during startup, and the fan is working while the compressor is not working, it can be preliminarily determined that the contactor is faulty. Because both the compressor and the external fan are controlled through the normally open contacts of the contactor, the contact operation is synchronous. If one is working and the other is not working, it can be roughly judged as contact failure. 2. Listen: Listen for a loud squeaking sound, if so, it may be due to (1) low power supply voltage; (2) There is dirt on the contact point or on the contact surface of the moving and stationary iron core. If you hear a clicking sound - the contactor cannot be sucked on, there are usually two situations: (1) the power supply voltage is low; (2) Insufficient contact suction force. 3. Smell: Smell if there is a burnt smell. If so, please check the windings and contacts. 4. Measurement: Cut off the power and remove the wire at one end of the contact control. Use a multimeter to measure the measurement. Press down on the three main contacts and another set of normally open contacts at the test end, and they should be conductive. Normally closed contacts should not be conductive. Put down the test terminal, and both the main contact and normally open contact should not be conductive. Normally, the closed contact should be conductive. The coil winding value is around 200 beats. Before measuring, one end of the line should be removed before measuring. 5. Short circuit: When the machine is turned on and the contactor is closed, if the press does not turn and you are not sure if the contacts of the contactor are damaged, you can use a pointed pliers to open them and use two pointed tips to short circuit the upper and lower contacts of the same group. If the press is working, it indicates that the contacts are damaged (note: safety should be taken when using this method). There is a wiring problem with KFR-7203LW/D. 6. Measure the coil using a digital multimeter with an ohmic range of 2K or less to see if the coil is open. If the circuit is open, it indicates that the coil is faulty. 7. Measure the normally closed and normally open contacts using a multimeter's ohm range of 200 (hold or power on the auxiliary contact points to measure the normally open). If the contact points are not in good contact, the resistance measured at this time is very high. Indicates poor contact of the contacts. If the auxiliary contacts are connected to a load, the voltage may not reach the rated voltage when measuring the voltage